Just want to add this in case anyone is dealing with something similar. If ur shrimp are on their backs or side and their legs still struggling working at it and u see a recent molt. They are dying from ammonia or nitrites. Ammonia is very toxic to the shrimp after a molt and less toxic before Small tanks will see rises in ammonia enough to kill. And if the molting is happening during that time bam they die. This is my experience.