That it's stayed quiet since you throttled Velero is a good sign, and it lines up with the concurrency theory rather than anything about the specific volumes.
Bumping dom0 RAM makes sense too, since linstor-satellite spiking to roughly 8,700 log lines around the panic suggests dom0 was under real pressure right then.
If it does come back, a xen-bugtool --yestoall bundle from the host that panicked, plus the Loki window you already have, would give @Team-Storage something concrete to line up against the DRBD side.
I'm not sure whether the real fix sits in Velero's pacing or in how LINSTOR handles concurrent create/delete, but the reproduction you've narrowed down is genuinely useful.
Fingers crossed it stays boring from here.
