Tumbleweed not booting: SDDM and kwallet crash

Since yesterday I can no longer boot my Tumbleweed. I updated to yesterday's and today's snapshot. I only see a black screen with a movable mouse pointer from SDDM. I checked journalctl and saw a crash with a stacktrace from SDDM. I then removed SDDM and installed lightdm. I could enter my password, but when the plasma session (both Wayland and X11) started, kwallet crashed. I assume some Qt or KDE library is broken. What details do you need to investigate further?