I had this happen on a map I hadn't even created a navmesh for yet. I just wanted to fool around on the map, but somehow got bots to spawn on it. They just stood where they spawned and as soon as I made contact with the enemy it crashed. So if you're having these problems on Falaise, either, you have no 'Aipathfinding' folder for Falaise or your Gamemodes have no 'StrategicAreas.ai' files.... If you're using the Falaise singleplayer files from these forums make sure you have everything installed properly and in the right place. If you don't have the Falaise singleplayer files, then your problem is that Falaise doesn't have official singleplayer support and you need to download the extra files.
On a related note, weren’t the static placements on Falaise competly redone for 2.26? I havn't played much of the map so I don't know...