Mat W

Yeah, this is 100% broken. The USB creator doesn't register any USB drives regardless of USB3 or USB2. Nothing I do can get around this. Sadly the previously created and working USB drive just got corrupted and not my unRAID server is down until I can figure out how to get a new one created which right now isn't looking so good. This is a MASSIVE issue!!!!!!!!!! I'm left without a working server. Unacceptable!

Just had the same problem BUT was able to resolve it pretty easily and without any data loss!!! So the problem I expected what caused by me manually moving the qcow2 image from one cache drive to another (w/ the VM stopped of course). After that it wouldn't boot and sat the UEFI Shell just like @flobbr did. After digging through some search results I stumbled across a post on the HA OS Community Forums. In the thread someone resolved the issue by simply deleting the VM but NOT the qcow2 vdisk. Then recreate the VM and point it to the existing qcow2. BAM! It boots just like it used to without any data/config loss. I know this is far too late to help the OP but for anyone currently having the issue (or in the future) this solution worked for me. Not entirely sure what actually causes the issue with boot failures after moving the image though.