AI stops working on Classic Mode random maps

Hi, I've been having a problem lately where... well, what the title says.

I'll be playing a 4-player random map on Classic Mode, the AI will function normally and attack me periodically... then around the Iron Age, everything suddenly goes quiet. I check up on their towns to see what's going on and find that they're not training any new military units at all. At worst, all their villagers will be standing around the farms and mines doing absolutely nothing, as though they all collectively went, "Nah, can't be bothered working today."

Should I reinstall the game or is there another way to fix this issue?