well , no surprise here...... the Iphone 6 only has a Dual-core 1.4 GHz .  Time to upgrade.     Most mid-range phone is much more powerful.  My modest Moto G7 Power is 8 cores at 1.8GHz

Today I encountered that problem on my second flight with Mini 2. I wanted to try a quickshot for the first time, the message popped up and the quickshot did not start. I was not able to get into other modes either, so I switched to video through the button on the controller. The rest of the flight was ok.
On the Mini 2 is the newest firmware, I use an Iphone 6 64gb. Iphone was under 30% of battery, in power saving mode, with charging from controller. I suspect that this is what caused the issue, I will try 4K quickshots next time with phone fully charged. If the Iphone 6 is really the problem, do you have any recommendations for some drone-only android alternative?

I had this happen for the first time on my "Drone Phone," and iPhone 6.  I think the newer versions of DJI Fly are more demanding.  Also, I started flying with 80% battery instead of 100% and the battery got to 45% when the message popped up.  And finally it was cold, which probably affected the iPhone's battery output.

I think it doesn't have to much to do with avail space on your device (although you do need space to save video)
I believe it's your cpu having trouble processing all that video which is causing it to bog down.
Look at the cpu speeds in these pics I posted.
I pad mini, and mini 2, i phone 6, all under 1840MHz
I think we need something faster like in the 2000s
So it looks like I'm selling my ipad mini 2!

steelgtr3 Posted at 2020-7-25 12:39
Happens now on my mini 4 ipad. Never had a problem with my P3, P4 or MP?  Is the Mini 4 up to the task for the new app?

https://www.youtube.com/watch?v=ElNZXuNGu8w&t=130s

https://www.youtube.com/watch?v=ElNZXuNGu8w&t=130s
I think I have found a solution for those of us who have drones and use iPad to fly.
The Ipad model that I use is the Mini 4 and many times while we are flying a warning appears on the screen warning that "The CPU of the mobile device is fully charged. The related performance will be affected".
After looking, in forums and in videos, I have not found the reason or a solution to this annoying notice. I do not know if it can be harmful while we fly but at least it scares and is annoying because we do not know what can happen. Nor do I know if the way I have found to solve it is the best but at least it works for me and it has been a long time since the notice appears.
The video that I have made consists of two parts to differentiate since the DJI Fly application is installed for the first time and the second part is after a flight (This time the flight is fictitious, I have only connected the drone, but to see the result is going well.).
Every flight we do, the Ipad generates files that are what make the warning appear later. The point is to delete those files and leave the Ipad clean and there is no need to delete the application and then reinstall. While flying I noticed that every time I installed the DJI FLy App, the warning did not appear.
It has gone well for me and if someone knows another way, I will be grateful if they say so because perhaps there is some other way to get to the same point that I have reached, but in a simpler way.
If I have not explained myself very clearly, I will be happy to explain it again.
The first step is to deactivate the Cache of the remote (Radio Control). Camera ---- NO Cache while recording (Disabled)

Had the same on iPhone 7 Plus today
Iphone 7 plus 256gb.
I couldn't control the drone for five minutes or more.

Happens to me too, every time with the  iphone 6....probably the sqme cause

Hi

I had the same problem with the message CPU fully loaded and phone shut off mid flight out one stage and I had to fly the drone back with only the controller. I did what Jody B said and seems to have been the battery that was causing CPU to be throttled.

I had the same problem today with my IPhone 7.
Here is what I did. I closed all running apps. Then I put it in airplane mode.  Charged my batteries and went out to test it. Not a signal glitch threw two batteries.
Those running apps take up memory.  Co close them out.
Doug

lherba Posted at 3-19 06:21
https://www.youtube.com/watch?v=ElNZXuNGu8w&t=130s
I think I have found a solution for those of us who have drones and use iPad to fly.
The Ipad model that I use is the Mini 4 and many times while we are flying a warning appears on the screen warning that "The CPU of the mobile device is fully charged. The related performance will be affected".

Hi
I have Mavic Air 2 and iPhone 6S 128GB.
Got same issue “Mobile device CPU fully loaded”. It just got worse and worse, leading to that it was impossible to fly even. I cleared Video cache as you said. It helped me, issue are now gone. I also disabled video cache in settings. Thanks and have fun

I know this is old but for future Google searchers (like me)... This is not a storage issue. It doesn't matter if the phone is a 500GB model or a 16GB model. This is a CPU issue. The CPU is working as hard as it can and it's not enough. Disabling video cache doesn't help because it frees up space. It works by not making the phone write the files.

Don't worry about how much storage your phone has. Just don't make your phone do too many things at once.

Yeah better buy second hand samsung with ram at least 4GB and with octa core CPU. Its cheap now anyway. As long as the port are not damaged..it works well. I use samsung A8(2018). it works great for DJI Fly app

Seen similar recently on much newer/capable mobile hardware, and also on the Go 4 app I use on the Mavic 2.  Can't confirm if its always iOS or if I've had it happen on my Galaxy...

I have a Mavic Mini and iPhone 7 (32 Gb), I just updated my iOS to 14.6 and on my first use after the update, I started getting the "Mobile Device CPU fully loaded" message. I never saw this message previously after 6 months and 50-60 hours of use. I've closed all apps, rebooted my device, cleared my cache and so far no resolution. I have not tried turning off device video caching yet.

Hi, I am getting same message with a mavic Mini and an iPhone 5s, never used to get it and I am getting an increased lag between the phone and the drone but not from the controller - any ideas?

On my Ipad mini 4 DJI FLY causes over heating in a sunny day...  Message Fully loaded and a incredible delay in the feedback image. That´s Horrible.,...    But it don´t happen with DJIGo4 in the sabe conditions...  That´s sad!

I don't use an iphone for flying (Moto Z3) but it could be related to purposefull CPU throttling in IOS. Older phones such as 6 and 7 and having older batteries, over time will begin autothrottling and will run with reduced performance. Here are some links that explains autothrottling and how to disable it. If I am right, this should take care of this.

autothrottling link

how to disable

Like I said I do not use IOS so I cannot check the veracity of the above but I do hope this helps.

FWIW: My Z3 does nearly the same thing but is based on remaining charge, not age of battery.

Hi, someone managed to resolve the message issue: Mobile device CPU fully charged. Related performance will be affected.

JodyB Posted at 2019-11-21 13:46
You started this. I trouble shoot my way. From the beginning. Square one. Don't like it. Don't butt in. You haven't contributed anything anyway. So who needs to grow up and get off their soap box?

He simply stated a FACT you are acting like a small child with his hand in the cookie jar, you obviously never understood the post you were replying to or you wouldn't have suggested the user do EXACTLY what he just told you he already tried. Get off your high horse and simply try to help.

aairon Posted at 12-18 06:34
He simply stated a FACT you are acting like a small child with his hand in the cookie jar, you obviously never understood the post you were replying to or you wouldn't have suggested the user do EXACTLY what he just told you he already tried. Get off your high horse and simply try to help.

LOL, you are amusing aren't you. To think you are any better than anyone else. I don't have a high horse. Never have and never will. You don't like the way I troubleshoot, move on like I am right now.

Same happens with my iPhone 7 occasionally. New phone only used for DJI Fly app. Full load CPU message comes up almost immediately. I bring the aircraft back on RTH then restart everything. It is intermittent so I am thinking software bug.

My dedicated iphone 7 settles when I leave it on with no apps running.  I only get the messages after starting the phone.

This week new iPad 9 arrived and seems to do the job even though it is not on the supported hardware list.

steelgtr3 Posted at 2020-7-25 12:39
Happens now on my mini 4 ipad. Never had a problem with my P3, P4 or MP?  Is the Mini 4 up to the task for the new app?

In my recent experience, the Ipad Mini 4, while able to download the Fly app, doesn't have enough speed/processing power to fly my Air 2S.
Had terrible video lag and video breakup until I tried using my Samsung A32 phone. Difference was dramatic and suddenly flying enjoyable again.

Now hoping the supplier will exchange the Mini 4 for something more powerful (and expensive!) otherwise £160 wasted. Very disappointing.

If you reset your phone or iPad it will go away
Press the home button the device and get to the slider that turns off the device. Do not turn it off. Hold the home button until the screen changes and asks for your pass word. That will clear the cpu and the message should go away worked for me.

Newbie here.  Flying my MP3 today on a iPhone 7plus 128g with 32 g available.   I did have other apps running and it was 0deg out.   CPU warning came on as usual but then a funny thing happened.. subject lost!   my phone screen went blank right after a wind and altitude warning.  At this point I’m 236m away and 121m up looking back on flight data.   I flew drone back to me as it was in sight and continued to practice maneuvers close to me until I could see my drone battery flashing one light.    So scary as it sounds nothing bad happened.   However it would be nice to know how to resolve the issue.   What I have taken from this thread is
- it’s not about available gigs
-use airplane mode
-turn off camera cache


Anything else I missed?   
Thanks