If you find that a VM is locked in Proxmox VM, you will not be able to use the normal methods in the GUI to interact with it. You won't be able to start, stop, or delete it.
If you find that a VM is locked, you will need to open a terminal to the host node and then issue the qm unlock <VID>
command. As an example, qm unlock 101
will unlock the VM in this screenshot.