I'm sure there could be several causes.
I just had this problem, though. Mainly at low speeds as well. Took the cover off and realized there was sand in the area. Wiped as much down as I could, and then I took out the clutch arm (barely could turn it due to the sand) and cleaned that down with brake cleaner. Took the metal pin and ball out of the middle of the sprocket and reapplied bearing grease. Then gave everything, including clutch arm, a healthy dose of marine gearcase lube (only oil i had around that wasn't 2 stroke or WD-40
). Put everything back together and it oslved the problem.
As for your drive chain question, you'd have to set your motor to idle and then to start it you'd have to kickstart it by lifting up on the bike frame so the rear wheel was off of the ground when you started it. Then you would have to put the clutch in gear slowly, like a car. This doesn't sound very nice but it works. But I like being able to pedal. Makes starting easier, allows a 'limp home' mode and allows me to assist when going uphill. So technically you could, but i doubt you would enjoy it if you did.