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Date & Time: 30/07/2019
Frequency: First time was today
World name: Behemoth
Character name: R'uno Kray
Monster name: The First Beast / Therion
Class/Level: Dancer 80
Party or solo: Party
Area and coordinates: Amaurot

Basically, both bosses models were strange. I'll leave some screenshots to show, but to put in some word, The First Beast color was strange, and Therion was invisible. That was only with both bosses, any other monsters in the dungeon were normal as always, and for what I could tell, it was only those two. All Eden normal bosses were normal, and there was no other bugs that I noticed.
And before today's patch both bosses were normal.