The timing evidence here looks strong to me. Your second Grafana window is doing a lot of work: linstor-satellite.service jumps to roughly 8,700 log lines in the three minutes around the panic, well above linstor-controller at 926 and xapi at 460, and the priority chart goes red at the same moment. A backup that fans out volume creates and deletes across three replicas, landing on a DRBD race, fits what you are seeing.
Throttling Velero should tell you a lot. If the crashes stop with clientQPS: 3 and itemBlockWorkerCount: 1, that narrows it to concurrency rather than anything about those particular volumes.
For the logs question, a xen-bugtool --yestoall bundle from a host that has panicked is usually the thing people ask for first (https://docs.xcp-ng.org/troubleshooting/log-files), since it sweeps up the kernel side alongside the storage logs you already have in Loki. I don't know DRBD internals well enough to say which trace matters most, so it might be worth a mention to @Team-Storage. They can say what they actually need rather than have you guess, and a panic that reproduces on a schedule is a good deal easier for them to chase than most.
