I’m beginning to run into the same problem, also with an HP 840 G6. I’ve tried the kernel arguments, however it just says ‘not a valid indentifier’. I have a Samsung 850 evo M.2 Sata 6GB/s drive laying around which I tested with, along with an HP 830 G5:

830 + 850 EVO: Success
830 + Original NVMe SSD: Success
840 + Original NVMe SSD: Failure
840 + 850 Evo: Success

I compared the SSDs from the 840 G6 and the 830 G5, and they are the exact same model. So while it’s of course a very small sample size, it’s pretty clear that’s it has something to do with the 840 G6 combined with NVMe that’s causing the failure.

One thing that also only happens with the 840 G6 is that it shows the following message:

udevd[3088]: inotify_add_watch(6, /dev/nvme0n1p2, 10) failed: no such file or directory
udevd[3089]: inotify_add_watch(6, /dev/nvme0n1p1, 10) failed: no such file or directory