hi Christopher Zdyrski ,

It looks like a fungal contamination to me.

Using antifungal agents might help.

Hi, Christopher Zdyrski

It looks like a cell death aggregation.

But I suggest:

Cut the point of yellow pippet tips and try catch up the aggregate.

If the mass are a fungical contamination, you can try coloring with cotton blue or just saline solution on a glass blade, besides that, you observe the border regions to search sporous conformation or any other structures.

If the mass are a cell death aggregation, you can use trypan blue to exclude this possibility.

I hope it helps your group!