Actually I think I may have found the answer. After browsing this forum, it seems Q3 AI doesn't have the ability to use certain OA weapons (missionpack weapons? Or something like that). And while playing I get a lot of "Error: Weapon number out of bounds" (or something like that) messages. So it may be that the models get stuck whenever they encounter a weapon that they can't use.
Does that sound logical? Can anyone confirm for me?
I wonder if I can get round this problem by filling all open slots with bots
Even if they all have this problem, there will be so many bots blowing each other to kingdom come that as soon as one gets stuck, it will be respawned.