RP4VM 'Enabled with no transfer' and 'user volume problem'

Following a network problem (now resolved), during which there was disruption to the inter and intra cluster connectivity we now have about 10 CGs that are stuck in an error state and "Enabled with no transfer".

Digging into the logs we see messages like these:

Transfer (GlobalCopy(SiteUID(0x4838036e99284278) 0) ) = Yes (unstable) - can't resync - user volume problem - Volume issue. Site=vcenter, RPA3, Device=[xxxxx, prod, CG_xxxxx_xxxxx_xxx1_0_0_
scsi].

This is being reported for many volumes accross multiple CGs, unprotecting and re-protecting potentially hundreds of VMs is not an option and we've already tried the basics of rebooting the VRPAs, disabling and re-enabling the groups etc.

Other than these errors the target VMs seem fine and boot up/shutdown with the CG, get reneamed .copy/.shadow as needed etc.

Other CGs in the same cluster, running on the same VRPAs and ESXi hosts are not having any problems, so its not a global problem.

Any thoughts?