Cant complete Einhar first beastiary even after him showing up to capture

Me and my friend are doing playthrough and for some reason he cannot complete the first bestiary, we are on act 5. ive tried everything to try to nullify the "bug" or whatever it is and we cant seem to figure it out. Any suggestions are welcome, thank you!

What do you mean with "first bestiary"?

Bestiary is just a mechanic, that Einhar is sometimes in your maps and you have to hunt down a few specific monster. After that you can sacrifice the monster in Einhars Place for currency or items.