I really wanted to like The Strange Affair of Uncle Harry, but I just couldn't get into it. Honestly, I thought that Sanders was miscast in that movie.
I haven't seen the other one you mentioned.
He might seem miscast if he's not playing a cad. LOL But I found him to be very effective, and he provided a good contrast to Geraldine Fitzgerald. It's one of those films that was forced to have a different ending than the stage play upon which it was based, in order to please the production code office. But the revised conclusion gives it a truly Hitchcockian twist.