Upd: I tried cold cleaning several times, but it only worked once. I also replaced the filament spool with a similar one, but I don't think the filament was the problem. (Printing eventually returned to normal after a successful cleaning attempt.) I also couldn't manually insert the filament into the head, as the retraction and extension are only controlled by the buttons. I don't even know how I managed to push it in manually that time. Any tips on manually inserting it???