The issue seems to be that you somehow have the "random" crown selected for custom characters (which share the save data), logic for which was never finalized because it was not pickable via UI anyway. Opening the loadout and picking other crown (e.g. "none") fixes the issue. I'll see about doing something with this for next update though.
Error text had no relation to the issue whatsoever, likely shown due to absence of debug information for part where the issue occurred.