I’ve searching for a solution to this problem for a really long time and found many posts about them from back when 4.11 was released, found no solution on those posts so far.
The problem is: using distance field ambient occlusion activated, objects that have checked or unchecked the “affect distance field lighting” option leave a black trail on a shadowed surface, happens on surfaces both affecting DFAO and not affecting DFAO, like this:
https://streamable.com/4t0w8!
And doing a first person game and watching this up close is really jarring, this is how it looks with dfao activated on the object just for reference: https://streamable.com/qabpg