Thanks for pasting the whole log; that made this much easier to chase.
Wild guess, but I think this may be a regression from PR #10124 ("replace vhd-lib calls with abstract methods"), which was squash-merged onto master as adecd7306 on 2026-09-11 at 09:42 UTC, just before your 202609112300 nightly was cut. master is still sitting at 99312eca2, with no fix (if any fix is needed, I'm out of my depth in this area) after that commit that I can find.
Reading the code on master, the transfer step now checks the VHD it just wrote and passes that data-directory path along while the .alias.vhd doesn't exist yet; RemoteVhdDisk.init then refuses a directory path that isn't an alias. I could easily be wrong about that, though, and thread 11875 is a reminder that this same message has had more than one cause.
If, by any chance, I've got it right, it would only affect repositories with "store backup as multiple data blocks" enabled. So does it also fail on a repository without that option?
Rolling back to a commit from before yesterday morning should get you going again in the meantime, and it's probably worth mentioning @Team-XO-Backend so the people who own this code see it.
And if I've made a total fool of myself with this "analysis", so be it.
