VNAV disconnects at each waypoint using RTA?

[MDFlier 2,031]

I set the last waypoint on final as the RTA waypoint with the time set to 1 min prior to my scheduled arrival. The flight started off perfectly and the RTA progress screen was showing everything running according to the schedule in my flight plan. I reached my cruise altitude and it seems like everything started gradually deteriorating. As soon as I crossed my 1st cruise level waypoint I saw a "VNAV disconnect" message on the FMS. I re-engaged it. Second waypoint, same situation. This repeated until I started my descent. The next problem that appeared was that I could not swap the standby frequency to active on either NAV 1 or NAV 2. I tried the alternate comm stack (click on the mic button) but could not swap them there, either. It was a cascade failure from that point on. It felt like a memory leak issue. I tried another flight using RTA and had similar results. I have since uninstalled and reinstalled the NGXu and tried a few flights. It made no difference.

Has anyone been able to successfully complete a flight using RTA?

Edited February 21, 2020 by MDFlier