No credit unique monsters

i killed foulwing and no creedit on my protector of tristam

Please read #2 of sticky post Things That Are NOT Bugs

If Foulwing wasn’t the last monster, just continue hunting other monsters. It will still finish even if the check boxes are not updated.

are you sure about this i killed blooodgutter to

prntscr com/qjbp3m

Yes.
Forget about the achievement window. Keep track the list yourself.
That was how I did in previous year:

Level Monsters
2 Shadowbite Rotfeast the Hungry
3 Madeye the Dead Brokenhead Bangshield
4 Gharbad the Weak Snotspill Blacklash the Burning
5 Bloodskin Darkbow Foulwing Shadowcrow
6 Deathshade Fleshmaul Bilefroth the Pit Master Bloodgutter
7 Blighthorn Steelmace Gorestone Nightwing the Cold
8 Firewound the Grim Zhar the Mad Baron Sludge
9 Breakspine Brokenstorm Oozedrool
10 The Flayer Goldblight of the Flame Blackstorm
11 Bluehorn Fangspeir
12 Viperflame Viletouch Lionskull
13 Warlord of Blood Rustweaver Witchmoon
14 Steelskull the Hunter Graywar the Slayer Stareye the Witch
15 The Vizier Red Vex Blackjade
16 Sir Gorash
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I have killed Shadowcrow several times and more missing bosses on the list but many of them failed recording. One thing i detected already the door which actually should unlock by the stones does not open even though i can easily do the other side it stays locked.
So it IS 100% bugged I have walked all parts several times on lvl 5 but nothing changes.

So i am trying again to kill the missing ones and one suddenly showed up.
after i had killed it like 7 times the shadowbite one on lvl 2.

I am redoing the dungeon again to make sure i have killed again all and see if it now will report done or not, but i guess it will not work again.

It is not a bug. Read the sticky link at top.