I've experienced the same problem with nvidia-legacy drivers. To return the session, you need to SSH to system, unlock the session via loginctl and switch to original VT to return the session.
Recently, I've changed my hardware and transferred the disk which I installed the system, everything went to normal without touching anything. It's very likely that nvidia's proprietary drivers are the main reason here.
signature.asc
Description: This is a digitally signed message part.