I've got multiple Betamaxes with seemingly the same issue...

[ARC Tech-109]

Threading ring is most likely jammed up with dried up grease, common issue with 80s vintage electromechanicals. Sanyo does things a little differently than Sony on the Betamax format in they unthread the tape when not in play/record mode and there's a little rotary switch to tell the microproc the position of the threading ring. Often times these are dirty inside and need a good squirt of DeOxit or similar contact cleaner, Sanyo used a glass fiber infused nylon threading ring in those so you want to be careful with how you attempt to move it around, easily broken and very difficult to find another. I have the Sanyo SuperBeta HiFi (VCR-7250) so I'm familiar with the problems, I'm assuming you have either the VCR-4400 or the 4600 decks or both and while they're not terribly difficult to work on they're not a good quality. I've owned my 7250 since new and used it for the audio quality (better than VHS HiFi) and more than once had to lift the top to rescue a tape.

I don't know who this Mr. Betamax is or anything of his reputation, I've been working on Betamax and U-Matic since the early 80s.