Sounds like the gimbal board is bricked. Granted, corrupted firmware can imitate pretty much any hardware problem, but the history you have documented fits the pattern of a failing, then failed main ribbon. The ribbon carries EVERYTHING between the camera (and the SD card) and the gimbal and drone. Including the IMU signal for the gimbal (the first set of codes you heard) and the updates for both the gimbal and the drone. There are something like 2 dozen small conductors in that very thin ribbon. When the ribbons first begin to crack, the broken ends sometimes mate up, and the camera will work for awhile. Then less often, eventually not at all. One of the first things to go is the ability to update the gimbal or the drone or both. As other conductors fail, other things quit working. It is even possible to get short circuits if the wrong conductors line up across the break.
It would be my advice to send it for repair. The ribbon is actually two ribbons in series, connected together under the left hub. The shorter ribbon is subject to failure when the pitch gets moved around too much. The longer ribbon gets damaged if the "Roll" joint gets moved around. Both joints can get a big workout during compass calibration.
Unfortunately, the ribbons are hard to install. Worse, they are hard to find. Especially the short one. The gimbal board might actually be OK, but maybe not. This would be an especially difficult and expensive Easter Egg hunt unless you find a shop that can identify any/all failed components. It could be only one, or it could be all three. The camera will have to be dismantled to know.