@Arek5 Thanks for the extra info. We suspect the root cause of the issue is the basic autopilot "PITCH" mode, and it seems like there may be some sort of conflict with the MSFS autopilot modes when the 146 is in an altitude capture state with "PITCH" mode and a lateral navigation mode active.
We'll reopen our investigations into this to see if we can get to the bottom of it.
Mark - Just Flight