Have you tried playing with the tracking to see if the Hi-Fi indicator lights up at all? I’ve had the odd tape where the sweet spot for the Hi-Fi not to drop out isn’t optimal for the video portion.

Believe it or not, screw-ups did happen in the dubbing facilities. It’s basically a room full of industrial VCR’s being fed the master tape. All it takes is a switch being in the off position. I’ve even bought a factory sealed movie only to find a totally different film was on the cassette.

Even stranger is an early Laserdisc I got in 1986 that didn’t have digital sound. (In spite of having the markings for it.) I didn’t discover this until I got a player with digital sound capability a few years later. I got another copy of the same movie which did have digital tracks. No evidence they are different pressings.