So I recently got the Mavic Air to replace my Phantom 3. I use the drone mostly for creating orthophotos of landscapes, so my camera setting is pretty much set to only aim downwards at the -90deg mark most of the time.

Not sure if others experience this but when I'm flying forward and I let the drone stop in mid air, the camera will jerk and shift up a little bit, by maybe a few degrees, so it's no longer perfectly at the -90deg mark. So I have to manually move the camera gimbal back to -90deg everytime I stop the drone. It only seems to do this if it involves stopping after forward motion. So even diagonals that involve a vector component of forward motion. But it is fine when flying backwards and camera stays at -90deg.

Now, I use litchi waypoints also, and when automated flights, the angle change after stopping still happens but litchi adjusts the camera again to 90deg to take the picture, but it could be a hit or miss if there is a delay between when the camera is finally back at -90deg and when the picture is taken.

Is this a bug and is it happening with other people? I guess not many people fly their drones always at -90deg for selfie stuff and so they might not realize.

Also, I discovered that the GPS data stored in the images of the mavic air lacks resolution so it affects precision of the geolocation.

I can confirm that strange camera behaviour. Look at 55 second in this video (the bird sound is placed by purpose to "explain" that strange camera movement ):

Interesting. Your video seem to show the camera jerking left and right instead?

Mine just tilts it up by a bit. Also my camera is pointing straight down at 90 deg too.

When looking at the drone, it's from the drone doing a sudden backward thrust motion to immediately halt the drone in place. I'm not sure if some programming error or whatever that the camera tilts up also when it does that braking action.

Yes quaddron, not exactly same behavior as in your case, but strange and annoying however. And it is not one time case. Just this time I did not cut it off from final video footage...
And yes - there was no heavy wind nor wind warnings.