We removed the ?ReachRadius on all our NavigateTo() calls. Something with that parameter is blowing up the NavigateTo where it never returns, leaving it stuck inside the loop but never continues execution. So the NPC just remains frozen. Its random though when it breaks, but easy enough to reproduce.
When you remove the ReachRadius from the navigation, you will need to monitor your distance to the target and end navigation when reached. In order to do this, you will need to spawn{} off your NavigateTo because its not async (which I thought it was before the update??)
After spawning the NavigateTo(), you can loop and monitor the distance to target. This approach has fixed all our npc movements.