Actually, only about half of them were actually switched on -- the rest I had tried at some point, but since there is no "remove" option in Gnome Tweak they were still in the list. For now I had to roll back to 18.04 because of another problem, but I'll come back to 18.10 in a while and check on this issue again. Apparently no one else seems to be affected, so it may really be just an unfortunate combination of extensions.
Actually, only about half of them were actually switched on -- the rest I had tried at some point, but since there is no "remove" option in Gnome Tweak they were still in the list. For now I had to roll back to 18.04 because of another problem, but I'll come back to 18.10 in a while and check on this issue again. Apparently no one else seems to be affected, so it may really be just an unfortunate combination of extensions.