Everything looks just as dark to my human warlock with Devil's Sight as it does without it.

Yes, this happened in earlier patches as well. However, I'm pretty sure I didn't get a disadvantage when attacking within the darkvision range granted by Devil's Sight. So I think it's just a lighting bug, not a game mechanics bug.

Well, it certainly does not work in magical Darkness, so not *just* a lighting bug.

Sad panda! There is mod that provides immunity to blindness if you have D_S but unfortunately patch 3 seems to have broken external mods also.

If you have a warlock with Devil's Sight, open the character screen, open the drop-down for the ability, and hover. I got:

ERROR: No Progression Description

ID:
00000000-0000-0000-0000-000000000000
Table:
00000000-0000-0000-0000-000000000000
Entry:
DarkvisionRangeMin(18)
Type:
DarkvisionRangeMin
Level: -1
Passive:
DevilsSight