In the dji go 4 app and go app my controller signal and hd signal will start flashing in the app. After a while the mavic will kick in RTH. I have to reboot the mavic and controller to make them solid again.

Things ive done to try and fix this:
Re link controller to mavic
Upgrade firmware
All possible calibrations

Any ideas?

Here is a video of it after it stopped flashing the controller signal. If the symbol stops flashing then it comes back with no signal bars until i reboot everything, but its clear by the video that it has signal. The mavic was about 10 geet from the controller.

https://youtu.be/ELAghlIj4Oc

Note: it will do this 3 out 4 flights regardless where I'm flying. Country side, city, park, indoors.....

Only thing i can suggest is to try the below things

1. Different USB Cable
2. Try an iOS device

Even though App has nothing to do with RC and Copter, heard these type of issues in the past due to bad USB cable ( Android ) / Lightning cable (iOS)

The flashing HD icon means that the signal for video transmision is weak. As RTH is started, this also seems to affect the general controller signal. I am also geting this every now and then and to my surprise the signal never got any better when the drone returned and got closer. I assume that this is a bug in the firmware because I cannot imagine why a good signal (5m away) is not again a good signal once the drone had a weak signal 500m away.

Back to your problem: As you alsways seem to have a weak signal something seems to be bad all the time. First idea: Have you switched your phone to flight mode? If not, its w-fi might be interfering with the controller signals.

Mavic Pro & Controler have latest firmware, latest version of DJI Go 4. I am also using a Shield K1 tablet with Android 7.0 Nougat. I also have been experiencing HD signal blinking. I have tried turning off the WiFi also the Bluetooth, several different USB cables and none of this changed the HD blinking situation.

I am tracking with dronenoob, if I start the flight and I have no radio interference and I fly in and around the area of my home and then fly out farther and the HD starts blinking, you would think when I return back to the area of my house where I had no signal interference, the HD would stop blinking. Did the mavic bring the interference with it back when it returned to my backyard? This is the confusing part for me.

Mine did this the first time, I believe it is caused by having download booster turned on my s7

Like the other poster said maybe try another android or iOS device as it seems that dji caters to them first then android uses get left with the scraps. Currently I'm using an s6 edge plus and it's working ok but I'm also getting the controller icon that flashes and the furthest I've been able to reach was 12000 something feet.

I have had my Mavic since November. I live in a remote area of Alaska with nothing to interefere with the signal.  I used to be able to fly it out over the inlet 4,000 or more meters with absolutely no issues.
It seems like every firmware upgrade brings more problems.  Now I can't fly out of my yard without losing HD signal and getting a "weak signal" alert.  When I bring it back the signal NEVER gets better, even if it is 5 feet away from me.  I can shut it all down and start over and it works for a few minutes.  I have been using an LGG4 since I bought the Mavic.  I have tried a Samsung tablet and it is the same now but used to work fine.  I think the firmware updates screw up everything.  I am going to sell my Mavic and get something, anything, other than a DJI product.  Right now, the thing is pretty useless.  I am very disappointed with DJI.
BTW, I have many, many flight hours with the Mavic and it has only started getting buggy with the last few firmware upgrades.  Unfortunately, you can't go back more than 1 or 2 upgrades.