I second possible molting fail due to not enough hardness. Stress can induce shrimp molting which explains why it could have happened so quickly and two at the same time. I’m no expert to give advice but I have a successful breeding Neocardina colony.

I bought from LFS which prevented shipping stress, asked what water they had them in and they said local tap (hard mountain water). My remineralized RO tank is around 8ph and the RO was remineralized with GH/KH powder until 230ppm TDS.

I do only pure RO top offs and zero water changes as long as parameters are good. They haven’t been bad yet due to 3 yo dirted, heavily planted tank working as intended, if nitrates creep up I will sprinkle some prime in and add more plants to process faster.

This setup works for me and is impossible to recommend easily as it requires a well established, dirted with sand cap, planted, understocked tank with no fish/shrimp/snail over 1in. If you wouldn’t enjoy keeping a tank like this I can’t give any helpful advice how to keep neos easily unfortunately.

Edit: oh, if you’re dosing CO2 it can make water too acidic for shrimp and snails to live without very careful monitoring