My acquaintance had the same problem for Linux DS.
There are two mods in use that can have a big impact: CBA, ACE3.
There is no problem in single play, but during MP missions on dedicated servers, the lower body of certain units freezes.
Attempts to shoot at the player by twisting the upper body in an animation sitting on a chair. https://imgur.com/a/IuI2Pcn
We have found that this issue reliably occurs on this server when the unit group's course of action is set to safe.
So I tried to work around this issue by syncing the trigger with the group leader and using setBehaviour to set it to Safe after a few seconds.
As a result, about half of the units worked fine, while the rest remained the same.
Waypoints, West/East, weapons, armor, class names, ranks, and animations are probably irrelevant.
I also had 100% the same problem when I copied the unit that had the problem.
There seems to be a cause for each unit. But I still haven't found any regularity.
If anyone has any information, please let me know. Linux DS, AI behavior, workarounds, etc.