I would agree that it is probably an issue with the bands getting weak from setting with tension on them for a while. When you stopped using it, did you leave any tension on the bands or did you unhook them?
If it was not for the door that is right there, I would have suggested going over the top of the sprockets and using a 2l bottle full of water instead of the bands.
I played with the bands initially but quickly went with the “gravity assist” method. I have not had a chain wrap or skip since (other than the time I forgot to hang the bottle bottles back on the chains).