SX70 with Retrospekt ND - Ejection Failure

I've been shooting my first pack of 600 film in my SX70 (Model 2) since struggling to get SX-70 film, and the final two images on the film pack (7 & 8) absolutely refused to eject. I took the ND filter off (obviously destroying that image) and the film ejected OK.

Has this happened to anyone else, or is it an isolated incident?