Aw man, I'm so sorry!!!! I didn't mean to totally gross you out and fuel disgusting nightmares!!! 😱 If it's any consolation, the leeches aren't that big (especially if they're young, they're the size of detritus worms), and they aren't like the ones you'd find in a lake or anything. I found a narrow gravel cleaner off Amazon and use that to siphon them out when I find them so there's minimal handling. Won't deny they're pretty gross tho!
So, my shrimp were mostly just disappearing one or two at a time until they were all gone. On occasion I would find dead adult shrimp but I'd never find any dead fry.
When my shrimp were at their peak, I fed them Glasgarten Shrimp Dinner and Betaglucan + Immunoglobin. Just a pinch went a long ways but found they were more active when I started these foods. My snails appeared to be more active and grew a lot faster too!
Are you using RO water or tap? Our local water fluctuates like crazy and I started losing shrimp at the beginning because of this. I needed to switch to RO water with Seachem Equilibrium... our tap water is insanely hard (sometimes over 400ppm, or 27 drops using Seachem's GH and KH tests) and found there was quite a bit of copper in it (sometimes as high as ~0.6mg/l). Maybe test for copper if you're using tap water - stresses shrimp out if there's enough copper in your water and can slowly kill them too.
Good luck... hopefully it's not leeches!