Please Help!! Bad Bamboo Shrimp Molt, tank parameters, or vendor?

[JTL]

I recently bought a bamboo shrimp online. About a week later and this is him in the photo. There are many factors that I think could have led to this and would like some help pinpointing the issue. Firstly, when he was shipped, the flight was delayed, causing him to be 7 hours late on a 85 degree summer day. He was also missing 2 legs, which grew back in a molt he had on the second day I had him, which leads me to my next theory. After molting, that cut bellow his abdomen and that growth on his head appeared (the growth started from a tear in his new shell that happened during the molt. My last idea would be my own fault. Im not the most experienced fishkeeper but all my parameters matched what I could find on these guys. Ph 7.3/7.4, GH & KH 6, temp 77. The problem with that is I previously had him in a 10 gallon because I bought him impulsively (a sin I know). I also had him with 3 guppies and 9 dwarf shrimp so the ammonia got pretty high at one point and I had to do about 3 water changes. I moved him and his whole community into a 20 gallon tank which housed my axolotl, but I got him a 30 gallon so I can get two when he's bigger. Which one do you guys think it is? By the way he is currently still alive and if anyone knows anything I can do to help him please let me know!!!