XP 12.0.9 RXP 6.2.1.1 autopilot NAV mode disengages

I'm running X-plane 12 with Reality-XP GTN 650 or 750 6.2.1.1 (latest).

I'm using the stock C172 G1000 in XP12.

If I have a flight plan with 3 way points (including the source airport), after the GTN completes the first leg with the AP, the AP horizontal navigation disengaged. The workaround is to turn hit the NAV button to get the AP going again ont he second leg. I also notice that only the first leg had been sent into the G1000's flight plan by the GTN, so that could be related to the problem.

If, on the other hand, I don't use the GTN at all and instead do everything with the G1000's (flight plan + AP), the problem naturally does not occur.

So this seems like a GTN bug.

Any suggestions?

Thanks.