Same issue I posted yesterday and spent a few hours debugging w/ out a solution. I assume you are running a nightly build and not the beta? Beta has no issues deploying VMs, seems the /usr/lib/python3/dist-packages/middlewared/plugins/*.py has changed since the beta.
Given it's a nightly issue may not receive any feedback from devs. In the interim if I find a solution I will post...
Other than the VM issue, been stable for me.