Not everything is always going to run smoothly, but much will, what I will look at here are problems which come up from time to time and how to go about solving them. Just some suggestions here
i) Check water parameters. Is everything ok? If not, is it possible there is some contamination. Something died at the back and decomposing?
Something containing copper, for example?
ii) Do fish look as though something has bitten them? Occasionally live rock contains predators which may be nocturnal and perhaps came as larvae or young animals. They may be hungry, Mantis shrimp you may hear, crabs you will not. I've had both in live rock.
iii)