Chromis are very sensitive as damsels go, when I've had any issues in the past they always seemed to be the first affected.
I would even say they are not the best damsel or "starter fish" as some people use damsels for(not recommended by me)
W/out knowing specifics about your tank my guess would be they might just be sacred in the new tank, maybe.
Some people swear chromis fight till one is left, or pair up and kill the others.
I've had great luck w/ them myself, and mine do "shoal"(the correct term) though I think it may be due to my always having tangs/larger fish which they may feel threatened enough to do so.
My longest lasting group were 6 I had 6 years and lost them to a heater failure way back, but I've had other groups long term as well, and in both odd and even numbers(another myth IMO)
Don't rely on LFS testing your water, you should have your own kits, and try to leave the room or distance yourself when feeding, see if that helps.
There's a fine line between owning your tank, and having your tank own you!_________________________________________
120G SCA starfire, tunze 1073.02 return pump, Geisemann reflexx 4xT5, 2x panorama pro LED strips, 2x Vortech MP 20's, 40g sump w/ fuge.