Hello
There is a simple answer to your problem.
Remove the sprocket cover and you will see witness marks on the inside of the cover between the two short screws. This is where your chain is binding against the cover. Take a small angle grinder and cut out the section between the two short screws, completely. You will have no more issues after doing this. I have experienced this on the first few bikes I made and ever since I have cut this section out and 261 bikes built, later, no issues.
Irish Martin