cannot open strongbox in valdo map

i am in crimson temple T17 valdo map.
to complete map i need to open all strongboxes.
i clicked strongbox killed monsters however strongbox didnt open. map tells me that there is 1 monster remaining. ive searched whole map but i cant see it. i think it stuck somewhere and he needs help.
thank you.
https://imgur.com/a/7lC8Aj6

no worries i exploded corpses with offering and it somehow opened. there was sanctuary of thoughts forbidden flesh. glad that i didnt stopped attempts to open it :)