I am currently using the QHYCFW2-US-M (36mm unmounted) and it has worked flawlessly for me. When I upgraded from the QHY9 to 22 I either needed to change cables or run it via USB. Theo sent me a document to allow it to work via USB, took 5 minutes and have not had many problems.
I have found that if I get impatient and don't let it stop moving before sending a new command it just continues spinning (serial command messing up). My own fault for being impatient. Just a matter of disconnecting the USB to let it reset, or just waiting for it to stop before issuing another move
