From what I was able to see in the other posts, the problem is truly on the vPilot side.
Strange AI pushback behaviour (pitch) - Support / Pilot Software - VATSIM Forum
Nose high GSX pushback by others on VATSIM/vPilot (fsdreamteam.com)
Let me quote:
"WHY it might have happened. This is a guess (that’s why I used that term), because I cannot possibly know much about vPilot code, but since I KNOW we have different code when dealing with the standard Pitch variable through Simconnect, which is handled differently in MSFS compared to FSX/P3D, I think a possible reason for this is that vPilot uses the same handling in FSX/P3D/MSFS without accounting for the differences in MSFS (the standard multiplayer mode clearly does), and if this is the case, it’s normal that reading that variable from vPilot and using it as in FSX/P3D would surely cause the pitch to be completely wrong.
With the following information, it should be clear there’s nothing we can do from our side to fix this. We are not transmitting anything over the network, we are just setting a variable that is clearly correct locally, how it’s transmitted and received (standard Multiplayer or vPilot), is completely outside our control."
“I’m befuddled. You loaded XPilot in X-Plane 12 and had the exact same issue, so you believe it’s a GSX issue? As far as I know, GSX doesn’t even exist in X-Plane. In fact, I don’t think FSDreamteam even has any X-Plane products at all. Given the above, how would GSX cause an issue in a simulator that it was never even designed for.”
Ah, thanks for the explanation. I have missed this.