Need assistnace with unlock Last Relic Slot

I have a problem. I need Unlock last Relic slot to complete challenge. Need to Complete the Mausoleum room in the Sanctum Necropolis(check screenshot) for unlock relic slot.I have completed Mausoleum twice
Proof : I have killed twice Colossal Lithomancer (Sanctum Necropolis: Mausoleum)
Screenshots:
https://ibb.co/XW4DyQ8
https://ibb.co/9gvx7y4
https://ibb.co/bFGDj2L

I have completed third time n slot was unlocked.