There are no other jobs.
I've now spun up a completely separate, fresh install of XCP-ng 8.3 to test the symptoms mentioned in the OP.
Steps taken
Installed XCP-ng 8.3
Text console over SSH
xe host-disable
xe host-evacuate (not needed yet of course since it's a brand-new install)
yum update
Reboot
Text console over SSH again
Created local ISO SR
xe sr-create name-label="Local ISO" type=iso device-config:location=/opt/var/iso_repository device-config:legacy_mode=true content-type=iso
cd /opt/var/iso_repository
wget # ISO for Ubuntu Server
xe sr-scan uuid=07dcbf24-761d-1332-9cd3-d7d67de1aa22
XO Lite
New VM
Booted from ISO, installed Server
Text console to VM over SSH
apt update/upgrade
installed xe-guest-utilities
Installed XO from source (ronivay script)
XO
Import ISO for Ubuntu Mate
New VM
Booted from ISO, installed Mate
apt update/upgrade
xe-guest-utilities
New CR backup job
Nightly
VMs: 1 (Mate)
Retention: 15
Full: every 7
Exact same behaviour. After first (full) CR job run, additional (incremental) CR job runs results in one more 'unhealthy VDI'.
I've engaged in no other shenanigans. Plain vanilla XCP-ng and XO. There are only two VMs on this host, the XO from source VM, and a desktop OS VM which is the only target of the CR job. There are zero exceptions in SMlog.
What do you need to see?