I think maybe u should NOT feed your animals right before you put in new animals! Looks like you're putting your shrimp into feeding mode, then dropping in the snails in for desert...like jumping into shark infested waters during a feeding frenzy. I've never seen my cleaners do this, but then again I've never fed right before adding snails.
What I do is if I'm putting new animals in that may get eaten when they first enter the tank, I turn the lights out while I float the bags. Everybody seems more calm when the lights go out and it works for me.
Sorry to hear about your losses btw
