Red Three was played by a British woman but voiced over by an American man.

Luke's lightsaber was portrayed by four different props with small differences, and even some small dimensional differences. The one sticking up of R2-D2 lacks a knob at the end of the emitter, which the other props have.

There are at least three different lightsaber props for Darth Vader. The one he throws is unique for that scene and the blade is coming out of the back end. The prop held by the severed hand is also unique. In all other shots, Vader is using a prop like the one in ESB.

Han Solo wears restrains when he is frozen in ESB, but not when he is thawed in ROTJ. (This continuity error would be easier to fix in ESB, though.)

Bantha herd (SE...) looks like a cut and paste job.

BTW, there is a long thread in the Fan-Edit forum called ESB and ROTJ Wishlist where lots more errors are mentioned but there is a lot of other stuff to wade through.