We have experimented similar problems lately, using Proxmox 7.1 with kernel 5.13.
We use both Ceph and NFS (FreeNAS 11) over dedicated 10Gbps networks (one network for each type of storage).
We have experienced some disk corruption on different VM, always on NFS FreeNAS storage. There's nothing to do with the VM disk, there's no partition information on it, so we need to do a restore from a previous backup.
As we don't want to do important changes along the summer to avoid new possible problems, we have moved a lot of VM from NFS to Ceph. It's only a workaround but we have less problems now.
By your messages it looks that it could be a kernel problem, but I'm not sure. I suspect the VM disk slowdown caused during the PBS backup (using a slow storage) could be an important part of the problem.
We will probably wait until last days of September before upgrading proxmox and doing changes, but it will be great to have more information about this and how to monitor NFS problems.