Whenever I rotate, the gimbal is slow to react. When I do any kind of rotations, the camera view starts to tilt relative to the horizon. When I stop the rotation, it can take up to 15 seconds for the camera to become level to the horizon again. The best example is in this video at about the 3:10 mark. I do a hard 90 degree spin, and it takes a good 15 seconds for the camera to become level with the horizon again.

So is this a hardware issue, or do I have a DJI GO 4 setting problem?

looks like a setting issue if no errors about the gimbal at the top of the app next to the DJI logo.  

if no errors then go into settings and reset the gimbal settings and camera settings i guess see if that fixes it, then if it does go back into the settings and tweak it if you want smoother slower cinimatic shots..  or if not then enjoy default..  

Have you calibrated the gimbal on a Level surface?

Just to verify, is there any impact damage before and what is your gimbal mode? Is it Follow mode or FPV mode? Please help to confirm and please try to calibrate the IMU, gimbal and reset the gimbal settings. Test again and keep us updated if the issue persists. Thank you.

I had the exact same issue. It happens after my mavic hit the wall and fell from 5 feet high. The problem is then fixed by simply re-calibrating the gimbal. Hope it helps!

I get the same thing (P4P). 10 seconds to level whenever turning - even when no wind. IMU, compas and gimbal calibrated. All settings reset. Never had a crash or anything line that. My drone is basically useless for filming and doing spherical panoramas etc.

It wasnt like this when i first got it. Just slowly became like this.