[Resolved to not pursue] Very slow luks password entry

[marteng69]

@user00

That was my first thought. But note that I excluded that possibility. As noted initially:

Also, I booted the Endeavour live media and was able to use cryptsetup to open the luks volume in but a second or so.

Did you install EOS with btrfs as fully encrypted installation?
If yes, your running into the problem, that grub is f…g slow in opening the encryption.
See also: Btrfs + LUKS via tutorial = Slowwwww boot time
Especially here