I ran into this issue with 3rd party models and found the solution mentioned above about a month or two ago.
However, this is also happening to me with default template projects (using the default engine mannequin), and I noticed that it seems to occur if I switch from Medium quality to High without restarting the engine. Restarting the engine after changing the quality slider seems to fix the issue.
I’m wondering if there is some sort of cache that isn’t updating or invalidating properly?
edit: Well, not even an hour later I’ve been exclusively working in the engine on High and the shadow residue thing is still an issue with the default mannequin. 