Life flask / health is bugged with darkness.

I have no idea what is causing this bugged interaction. I have nothing affecting life flask usage, yet I will take life damage use the flask hotkey and it heals me but then I can no longer use it after that even with my hp not full.

I just tested further and in the clip I was trying to use the flask but nothing happens, when my darkness reaches 0 my hp suddenly became full when I do not have anything to heal me like that.

I took a video here
https://streamable.com/8zz3aa?src=player-page-share

Edit: More testing lead me to see that even though my life flask has enough life regen to heal me to full it does not, this made me think it's just visually not full but devouring a corpse will then regen my health back up to full so I'm really confused what's going on...

https://streamable.com/ffk0so
Another weird interaction, I died but then suddenly I'm back alive with no exp loss etc, is this some mechanic I'm unaware of?