I'm not sure. My guess would be a former human manager was building the team up and quit. I would also assume that when a manager quits, his/her team isn't cleared until the team is appointed to a new user.
It should be cleared transfer list when players with salary roughly above 10k (maybe a bit less) hit the market. Maybe it only happens when teams became bots through inactivity and nto if for other reasons, dont know. If that you faced lsot its manger due to inactvity I would report a bug.