I also have something killing and eating snails in our 120g. Never see the culprit as I think whatever it is attacks at night. Only see the dead snails partly eaten the next morning, then a few days afterward, there's nothing left of them.
I know we're not dealing with an
Oenone worm because there is no slime covering any of the snails.
Snails have been with me for months in various tanks before amalgamating them into one back in August, so acclimatization isn't the problem.