Uber Cortex witnessed by Maven. Can't understand who's doing this mess!

So, i just came back playing after a few years and after the first map on standard i receved every single atlas point back, except for The Feared. I'll never understand how the game can be so dumb to forget what you did and what you didnt do, but still it is what it is and i have to do it again. So i decided to do Cortex witnessed by Maven for The Feared. Since i've never tried an uber, i decided to give it a shot. Uber Cortex witnessed by Maven.

Now, i realize i dont remember anything about the game but wtf is this? i dont remember anything like this. The arena is filled with those dark holes and they never go away. I tried to spread them but as you can see its completely filled at this point. I tried to check venarius moveset, maven moveset, the golem spawned by venarius, multiuple completely useless youtube videos so called "guides".. no one ever mentions any dark circle.

https://gyazo.com/d37fb5951e9093c69084a7a5de993074

So i was wondering, do you recognize this? Since i still have 4 portals left i would like to fix this if its even possible :) If its not, its not a big deal :)

Unfortunately, uber fights are a hard dps check. you need to kill them before the arena gets too cluttered.

Yes ofc, i'm not complaining or anything. I just asked "who's doing this mess?". I don't understand if it's the Golem, Venarius or Maven.. That's the question i asked :)

I think it's this guy's doing

https://poedb.tw/us/Twisted_Synthete

His quicksand most likely, a physical dot.

This is why I stopped building a lot of defences on my characters nowadays. It's a no-go if I can't even get 10 million by level 94. My main defence line is my number of portals.