Weirdly enough once you get to around day 60 visual indicators of day and night stop
Confirmed the issue.
When playing the vampire special, the lighting of the normal rooms is disabled to allow for the spooky lighting on the vampire dungeon - and was not being re-enabled once the event finishes.
Quitting to the main menu and reloading a save does fix it (since it forces a reset).
I'll fix this in the next update, thank you for reporting!!