Hi vengerboy,
I’ve noticed exactly this happening in the 172 in NAV mode as well as several other aircraft. For me, it only started happening when I signed up to the AAU2 beta, and only when flying in external view, but others have tested for and seen the problem as well.
I started a discussion and poll on it in the AAU2 comments section here: Autopilot not working properly in External View - Aircraft & Avionics Update 02 Beta / AAU_02 Discussion - Microsoft Flight Simulator Forums
For me, it only seems to happen when using the external view / chase cam (I fly a lot of low and slow bush trips, and like to sight-see), and switching back to cockpit view resolves it, whereby the aircraft immediately turns itself onto the correct flight path.
I’d be really interested if you could review the linked thread, and add your comments to see if this is the same problem. Particularly any reactions or discussions you have had with the developers, as this could be the same problem or at least related.