I managed to make it occur after 20 mins of flight. I wouldn't say I reproduced the bug because I'm not sure what are the exact steps to make it manifest. The attached track file has the following flight profile (Radar Off, I don't think it's relevant though):
1. for 10 mins: TO from Batumi, single turn West, straight and level. Result: Not a degree of drift.
2. X mins of banked flight straight and level. Result: No drift.
3. up to 15:20 in-game: Immelman followed by straight and level flight. Result: 5 deg drift.
A video recording I took in parallel with recording the track. Not entire flight is included in the video.
bug F-5E attitude indicator 5deg error after 20 mins 2024-11-30.zip