My very fist guess would be that pathfinding fails due to projecting destination (or start) to navmesh failing. There has been minor changes to related code and it seems it’s a bit more strict now. If that’s the case the easiest way to address it would be to expand navigation query extent and that can be done by adding following to your DefaultEngine.ini:
FYI, there are other parameters a supported agent can specify. And you can have more than one witch will result in multiple navmeshes, one per unique supported agent.
In general the best way to debug AI issues is to use VisualLog. It’s not perfect (it’s a tool for coders by coders, so… you know… ) but it’s irreplaceable when it comes to tracking AIs’ state in time. Just run console command “vislog”, press “record” and start/continue playing. Let me know if you find anything interesting!