I believe that is a side-effect of the quick fix for the ladder bug which was even worse.
Usually you can heal it by walking onto the ladder again (may be a bit hard to find on the black map) or walk out of the black area using cursors.
as soon as you are out of the black the map heals itself.
Last edited by Drugar Stonesmasher on Sat Nov 14, 2020 8:07 pm, edited 1 time in total.
This bug is occurring literally since the moment they fixed the stair-freeze. But when Slightly and I tested it, it took a huge effort to force it to happen. Seems like it got worse, though.
in compairison to the ladderbug this is just a nuisance, because in 90% one can heal the effect.
I hadd just an additional strange effect:
Creatures of course can move on that black map and you can attack them.
After they are dead they vanish from the black map, but still continue to attack you.
On relog they are alive again, which is consistent with them continuing their attack.