Just want to make sure you have a chiller for stable temperature.
Good to hear that you have a DIY chiller.
Do please show us a picture of your tank.
I assumed it is just a piece of driftwood with moss?
I have plenty of driftwood and moss in my tank and hence it is impossible to count them.
Are you sure it is damselfly and not mayfly nymph?
Anyway, it is best to get rid of them if you are not sure.
As for your tank, don't panic over 1 dead shrimplet as no one can have 100% survival rate all the time.