If it does not free in persistent mode, then this could be the case.
How much (free) RAM does the host operating system have?
So you did boot in host live mode… Did you then start VMs in live mode or “persistent” mode?
When starting the host in host live mode it’s not really needed to start the VMs in live mode. I don’t think we currently make this clear in documentation. But perhaps starting VMs in “persistent mode” wouldn’t be really persistent since the host is already booted in live mode would help.
Related: