I just replaced my Phanton 4 with a Mavic Pro Platinum and the images/video I take don't seem to be writing to the card.
When I take the image, the controller reacts the same as it did with my Phantom 4, but when I connect the Mavic to the computer to uploiad the images there's nothing in the DCIM folder.
I tried re-formatting the card and the controller screen says there's no card.

I just took my first flight with my new Mavic, hooked by the way.  I'm not sure if your issue is the same as mine, but it sounds similar anyway.  I took a couple videos, no problem.  I took about 6 pics, but only one is visible in the photo file of the app.  I did have to relaunch the app due to it crashing, yes I almost had a severe panic attack, thought it would just say buy bye bye, hehe.  The app was up when I took the photos, are they lost?  This is my first drone.  I'm familiar with controls, and have been studying it all, but still have a lot to learn on the "tech" side.  I had no luck with the helicopters.  

Just pulled my card.  Everything is there when it's in the computer.  Must have been a glitch when the app crashed mid flight. Its quite obvious I'm a rookie.  Wish I could be of some help Photoguy.

You can go Into the DJI Go4 app when disconnected. When you get to the page that says Enter Device, look on the bottom and you’ll see Equipment, Editor, Skypixel and Me. Click on Editor. From there you will see Album  and Create...choose Album...below that you’ll see Videos, Photos and Album...your photos or videos should be in there...this is if you want to access it through the app....normally just take the sd card out and transfer your images to the computer...hope this helps