That happened to me from time to time during water changes. I wondered what it was.
I did have a lot of Vermetid snails. And I have read that the way these snails feed is by casting out a web to catch free-floating food particles. Then they eat by consuming the web and all it has trapped.
I can but it is difficult because it is kind of slimy and it dissipates in the water when I try to grab it… I’ve been using the turkey baster to get it out