I have seen similar but only on large swords, specifically Echinodorus bleherae. It is nutrient related, not anything to do with those small snails.
Sorting out such issues is sometimes complex and takes a bit of experimenting. In my situation, I have solved the sword problem by using Magnesium sulfate, pure Epsom Salt. The plants were lacking magnesium; my tap water is very soft, < 1 d GH, and the magnesium in Flourish is clearly not sufficient for such heavy-feeing and fast growing plants. And these swords are enormous, with 3 double inflorescences this past year, and now they're sending out more. Most tap water in NA has more mineral, mainly calcium and magnesium, which are both macro-nutrients. The sulphur in ES is beneficial too, another macro-nutrient usually found in tap water in sufficient quantity.
But this can have a price; I have previously over-dosed ES and in that situation the swords developed an iron deficiency and the leaves became clear between the veining. Took months to fix.
My point is that you have to be careful with dosing nutrients, as an imbalance is easy to create and can be detrimental; so assess what is in your tap water plus what you are adding weekly, and look for the likely missing link. But then go slow. Sudden changes can be worse. And crypts will most likely melt with any such change.