I'm sure the more experienced reefers can answer this better, but just I case it has been overlooked. Do you have algae growth, diatoms, cyano or anything like that. I'm wondering if you are getting false positives in some of your tests.
Personally, I would change out any canisters, filter media and then do a series of water changes over ten days. 20% every third day. Test your water (RO?), see what the norms are. Are you dosing? Could your products be expired?
There are a lot of easy things to look for, exhaust these options first just in case you might have overlooked them. After that, start looking at things like are you missing any fish, have any inverts or corals disappeared? Do you have some missing turbo snails?
After all that, they are SPS, they don't need a reason to do anything. They seem to do because they can. Good luck. Keep us posted!