It would appear that some 'More Attention to Detail' at the shop, prior to return shipping, could have eliminated this problem altogether.
I have had ample opportunity to experience this very same problem in my own 'Experiments' in decibel attenuation devices.
A simple twisting or turning the device on the end of the barrel a few degrees in either direction would 90 % of the time clear the problem. Too bad the guys at the shop did not attempt this simple test and solution prior to return to customer.
These end pieces are very Finicky sometimes.