That's the tilt (pitch) encoder. Barring some weird stuff we can talk about after the more normal stuff, here are some likely causes, in something of a descending order of probability:
1.) Loose wire at the encoder solder joints.
2.) Pin not fully inserted in connector. (loose or missing pin latch)
3.) Broken or shorted wire somewhere along the path (including at the wire pin connector)
4.) Bent / missing pin inside the socket on the gimbal board.
5.) Broken solder behind the socket on the gimbal board.
6.) Failed gimbal board component. (more probable in your case than for some, but not very likely)
7.) Bad encoder. (I've never actually found a bad encoder. But it's possible.)
The weird stuff is how the board interprets encoder failure signals. It does well if there is only one problem. But it gets confused when there is more than one (such as two crossed plugs). Sometimes the system only reports ONE code, sometime it reports all. We can do some creative troubleshooting if "non of the above" turns out to be the problem.