In the past week I think I've lost about 5 out of the 50 red cherry shrimps I have and they all seem to have the same problem some die trying to molt and some were only able to molt just they body part but the head part gets stuck. I just found one today with half of its head shell lifted up a bit. He's still moving big a little so I put him in a separate tank by himself to see if he would make it or not. Before some of them die, they have a horizontal Crack from left to right side of their body (in-between were the head and body connects). I have a shrimp only tank(50ish red cherrys and 5 crystal Reds in 5.5 gallon tank with fluval underwater filter) that is planted and I use fluval plant substrate. The crystals are doing fine though. I feed them shirakura soft pellets every 2-3 days and white pellets by biomax or cucumber once a week. I also have a piece of catappa leaf in there.
These are my water perimeters:
Ph- 7.4 - 7.6
Ammonia - 0 (since I use prime, the only way to test for free ammonia for me was to get the seachem ammonia alert that sticks to the side of the tank)
Nitrite - 0
Nitrate - 5
Kh - 4 (drops before it turned color)
Gh - 5-6 (drops before it turned color)
Temperature - 23-26 Celsius through the day
I change water once a week with top water and use seachem prime to dechlorinate the water as well as fluval shrimp Mineral supplement since my water was really soft with no minerals. I also have a small Mineral rock in there.
I desperately need help since I have done everything I could including tons of online and in store(shrimp store that specializes in shrimp keeping) research but nothing is helping.

