This might explain it... 
/usr/share/sddm/themes/breeze

now only has one file in it... theme.conf.user

Where did the other files go?

On Fri, Sep 4, 2015 at 11:44 AM, Gerald B. Cox <gbcox@bzb.us> wrote:

My /etc/sddm.conf has:

[Theme]
Current=breeze
CursorTheme=breeze

prior to the most recent testing updates, was working fine.  Now
I get a blank white screen.  By trial and error I found I needed to
comment out the above lines to be able to login normally.