I know people say use the camera to format the SD card, but that's given me a LOT of grief - and I'm using DJI's reccomended cards.

I have spent some time testing this, and in my opinion, what works best is to do a full format on the card using a PC - it takes a while - then delete unused files either from the camera or computer.

The issue I had was that the card would record for a while, then it would sometimes not record sound, or sometimes ask to be reformatted - this was after formatting with the camera.

Hi, djiuser_vB7rsMeLSR1z. Thank you for reaching out and we're sorry for the inconvenience. May we ask what microSD card are you using and what is the current firmware version of your Action 3? Also, please share some sample videos showing the issue for us to further check.

I dedicate a sd card to the camera, and  never save files to it, I dedicate teh HDD of the computer for that after I finish using the camera.  I practice a Full format once a month.

the computer 64gb takes 30 minutes, then after completed I then do a quick format, and then to the camera, a format, and every day when ready to use the camera I format, then  when completed my  shoots, I then dump to the computer, and Delete all off the MTB drive, and the next  time. I do a format.   I do not put back files to the cameras sd card.

how I do noy work, and my card never has an issue

Fish

IMHO