Dear Developer,
I believe the first 30 seconds of this youtube recording describe the entire problem:
https://www.youtube.com/watch?v=sgdHpDp91eA
In words: the AI character literally walked through a wall.
This occurred on the default multiplayer game mode "Escape" (COOP, 10 player, map Tanoa). As can be seen in the video, it is one of the hangars on the main Tanoa airport.
The host was a AWS (Amazon EC2) cloud linux Dedicated Server running the current version of steamcmd and Arma 3. All 8 players were running the "Arma 3 Apex Edition", no mods on any clients whatsoever. Average ping was 21 milliseconds.
I do not know whether it's related to multiplayer synchronization, map geometry, or some form of "cheating" to fix AI pathfinding, so I placed this bug into the "Other" category.