By snail like, do you mean they had a shell on their back, or are you just talking about the big fleshy foot part?
Were they free-floating, or clinging to the tank/plants/rocks?
What type of fish do you have (and could these be egg clusters?)
How big are they?
If the only change you're seeing is a few of these things, I doubt they're bacteria. Generally, by the time you can see a colony of bacteria, they've inhabited every bit of the substance you see them on or in. In this case, I would think that, as dying bacteria produce toxins the same way larger organisms do, this would have changed your tank chemistry quite a bit. I could be wrong, though.
Another question. Are either of your fish acting strange? In particular, are they rubbing against anything in the tank. What you're seeing could be the dead adult version of an anchor worm (technically a crustacean).
I'm not saying that this is a likely suspect. Instead, by searching "white worm aquarium", this was about all I came up with. It could easily be something else entirely.
I would suggest making a worm trap as listed on this page https://www.algone.com/worms.php
and see if you can get any culprits. As I said, what you're seeing might be an adult or a deceased specimen. What you get with a trap will likely be alive, and perhaps more easily identifiable. You might not get anything, but if you do, you'll at least be able to identify it and figure out if anything needs to be done.
Geez, I didn't even think that simply.
I don't know if the shape you're seeing is solid, like the ram's horn, or if it's more like it was made out of a narrow line. If it's the latter, it might be a partial shell of a type of conical snail. I used to find these on the beach at Lake Pepin all the time. They look alien, but if you see how they're made (by cutting into a whole shell), it makes sense.