Missing ONE last conjuration

I have 139/140 conjurations. The last one is in exploration.

I searched everywhere.

Butterflies, vivarium, depulso rooms, flew over the whole map... Any ideas?

Update...

It was the GOD DAMN vivarium chest. The thing is, I already was there and opened it, but it seems like the game didn't get the opening move so it didn't register it....

I spent hours and followed the whole walk through from a youtube video and it was just that... I wasn't paying enough attention to it. I'm so stupid.

What are we learning? Look twice if the chest really opened.