I was running the snapshot from Feb 10th.
When applying the snapshot from Feb 13th (or 14th, unsure), I had problems with
nvidia drivers (see bug #1208645 ), as there might be a regression. In
addition, the "init bar", "menu bar", "task bar", or whatever it should be
called, has disappeared from my user.
I've worked around the problem with nvidia by manually installing the previous
version, and now all my screens are working fine, however the problem with that
bar in the bottom having disappear is still there.
I've created a new test user and logged it with it, the bar exists.
I've tried to kill the plasmasession and run it again, but that did not change
anything (other than I think it is crashing, because the background image did
not come back).

I have too many configurations to create a new .config directory and would like
to avoid this. Rolling back to my btrfs snapshot I created previously fixes
everything.

Please let me know which logs would be useful to debug this. Thanks!