The Proxmox backup uses a global lock file to prevent multiple instances running simultaneously. More instances put an extra load on the server. The default lock wait in Proxmox is 180 minutes. Depending on different virtual environments and numbers of virtual machines, the lock wait time may need to be increased. If the limit needs to be 10 hours or 600 minutes, adjust the option as follows:

lockwait: 600 

The lock prevents the VM from migrating or shutting down while the backup task is running.