Seems like a loading belt that is slipping to me. Fits with the "worked last time I used it" description as well. Should be pretty easy to find the belt, it'll be directly attached to the loading motor which is a separate DC motor or will otherwise obviously interact with the loading mechanism that you can see from the sides. This is super common on the JVC SR-VS30U (for it to have a loose or slipping belt which I'm guessing is a similar mechanism - if that were to be the case, you'll see the belt off to the right side of the loading mechanism that is not visible in your video.
You could either replace it with cheap ones (sometimes you have to use 2 at once to get the grip to be strong enough) from a variety belt pack on
Amazon, or you could also try boiling it in water for a bit in the hopes that it will contract some. Sometimes the plastic pulleys can have sort of oily residue that develops, so you'll want to clean that with alcohol as well. Also have heard of putting violin bow rosin on belts to get them to grip better which makes sense.
