I’ve had an issue with the chain wrapping around itself on the sprocket. I’m a novice novice…LOL. I get everything set up. Finish the calibration, then when it starts moving the sled the chain will wrap around itself on the sprocket. I’ve gone through this same stage a dozen times with the same results. I need more tension on the slack portion of the chain or something to keep the chain away from the bottom portion of the sprocket when it is slack.
I think you have diagnosed the issue correctly, more tension on the slack portion of the chain is the correct solution. The easiest way to do that is to adjust the length of the bungee, but you can find a lot of good solutions here in the forums using different types of bungees or counterweights