WH40K SpaceMarine2 RUNE AiO update always fails

I've tried several times now, but even when the game is fully installed and checks OK, the RUNE all in one update always fails part of the way through with this error:

"There was an error of unpacking in the module isxdeltaextract!"

I've tried turning WinDef off, no other AVs, run as admin, compatibility mode to Win7, shortened folder name, NVMe SSD separate from C drive, and yet the patch constantly fails with that error. I don't know what to do anymore.

This is on a 7950x3D, RTX 3080, 128GB RAM.

Can somebody please help?