Hi! I'm having a very similar problem. I can't login after today's upgrade. I tried from a console, but it's the same, it shows the welcome message and then the screen is "cleared", asking for the login name again. The is no difference if I try to login with root user.
I was able to login with super user by booting with rescue mode, but I can't find any useful log. If I start sddm from this mode, the same happens. Any disk is near 100% of usage. Thanks!