Could be the tank isn’t established enough, these shrimps live off algae and bio film which is constantly produced in a well established tank.
Or it could be too large water changes, some species even fish can’t withstand massive changes and require smaller 20-30% water changes rather than 50%.
And last it could be something in the water that affecting them, maybe the parameters aren’t stable. Sorry for your loss tho
Do you have a strong filter flow? How big is the tank?
I would try varying the diet a bit more. I pulverize some freeze dried brine shrimp on top of the algae and occasionally stir up a bit of substrate to fill the column with particles. If you catch them walking around fanning the substrate then they likely aren’t getting enough food. Mine just sits on the top of the rock in front of my filter and occasionally picks some goodies off the pre-filter at night.
lucasmelonboy 
It’s the weekly 50% water changes. Inverts are very sensitive to parameter changes and a water change that big could easily kill them
Why are you doing such huge water changes so often? If your tank is properly cycled, water changes should rarely be needed.
Struggling to get out of the water is usually something with the water params. Ammonia/Nitrite/Nitrate?
What are you feeding it?
Could be the tank isn’t established enough, these shrimps live off algae and bio film which is constantly produced in a well established tank.
Or it could be too large water changes, some species even fish can’t withstand massive changes and require smaller 20-30% water changes rather than 50%.
And last it could be something in the water that affecting them, maybe the parameters aren’t stable. Sorry for your loss tho
Do you have a water flow they can get to?
Do you have a strong filter flow? How big is the tank?
I would try varying the diet a bit more. I pulverize some freeze dried brine shrimp on top of the algae and occasionally stir up a bit of substrate to fill the column with particles. If you catch them walking around fanning the substrate then they likely aren’t getting enough food. Mine just sits on the top of the rock in front of my filter and occasionally picks some goodies off the pre-filter at night.