Hello Mystic. I've not been able to find any information other than the fact that snails do leave trails. I checked for snail diseases and there was nothing mentioned about slimy residue being an issue as far as disease is concerned.
I have a feeling it's just what they do. I haven't noticed anything of the sort with my Mystery snails though.
I wish I could tell you more. Here is a link you may want to have at least to book mark for future reference.
Snail diseases and problems Apple snail FAQ
Ken