Bug report 1: The AI thinks building a trade yard is a high priority, even over removing ruins. Furthermore, building trade yards seems to be a higher priority in 3.1.0 than in 3.0.0. As a result, the AI can wind up being ruins collectors:
Bug report 2: The AI is poor at waging war. In the above screenshot's game, even as a ghoul unit was creating ruins, the white-outline force sent a single levy unit to try and defeat their northernmost province's lion nest. They're also more than willing to send a clearly insufficient force to attack a ghoul unit (levy only, equal or inferior numbers).
EDIT: Just after that image I took the empty land northeast of white-outline (carpe diem!) and exchanged maps with the blue-purple just northwest of white outline... who has four more ghoul units causing problems. Therefore...
Bug report 3: As of 3.1.0, the AI cannot handle ghouls.
LATE EDIT: I've seen that the AI obsessions vary. Sometimes they really want trade posts, sometimes they really want farms, but on multiple occasions I've seen an AI build the same building over and over in the same territory.