Photo is not very clear. Grab the snail and get better photos.
My guess is you’ve got nerites laying eggs on the other snails. Happens often as nerites love to lay eggs on hard surfaces, driftwood, rocks, shells etc.
Thank you I've been sick thinking I've created an unhealthy environment that's causing the shell issues. Thank youOof ! Your nerite went to TOWN !!
those are eggs for sure. They won’t hatch, they won’t harm the snail just leave them be . A little unsightly but kinda funny