Are you using fish as your login shell? I had a similar issue (though I was stuck on a black screen without a text cursor), and I think it was related to this issue https://github.com/sddm/sddm/issues/1592. I was using fish, ssdm, and trying to login to a wayland session.

The issue also does not exactly describe what you saw but I hope it's helpful. Unfortunately I don't have a solution myself, I swapped to using lightdm instead.