I like to think I understand what you are going through. The worst situations seem to be the ones you can't determine the cause so that you can fix the problem.
I had an unexplained decline a couple years ago. Wiped out almost all inverts - sps, clams, stars, most lps, entire cuc etc. Fish were "acting funny" / not looking good. Water quality was better than ever, spent a lot of effort trying to figure out what was going on.
I woke up at 3am one night hearing unusual noises in the living room. Looked at the sump and was like July 4 fireworks. Faulty heater was leaking current, we're talking bare wires in salt water by the time I discovered it. Didn't trip the GFI, lucky house didn't burn down.
I should have been happy that I finally figured out the cause. Instead, for 4 months I was so depressed I couldn't touch the tank. Didn't do anything but dump food in it just to keep the fish alive. I watched the algae take over. I considered the upsides of tossing in the towel - wife would be pacified, I'd have extra time, money, space.
Finally made the decision that I couldn't quite. I was going to get serious. We're talking ignoring the wife's complaining about how much time I spent on the tank, instead of trying to be discreet by working on it when she wasn't around. Not worrying about how much something set me back if it was needed to "do it right", instead of delaying needed equipment acquisitions or trying to mickey mouse it. I started by purchasing the best replacement heaters I could find, not the cheapest.
I've still had a couple bumps in the road, as we all do. But that's all I see them as - something to work past and keep moving forward. Taking ALL your fish out and putting them in a temporary tub on the fireplace hearth, while you let your main tank go fallow for 8 weeks to kill off an unidentified parasite, is no fun. It gets uglier when you loose half the fish, many favorites you've had for years. But it was an opportunity to make some changes to the main tank without the fish in the way. I restocked with different specimens to replace some I really wish weren't taking up bioload.
I just spent 10 hours TODAY, dismantling and removing my entire sump to fix a slow leak. Lucky it was on tile flooring. I switched some equipment around and made some other adjustments while I had it all apart. I'm happy about the improvements, have forgotten the water puddle.
You have a very solid setup that looks great. You know it has potential to be TOTM some day.
But it is young. We all know, only bad things happen fast in a reef tank.
And even when you do everything possible, there will be some setbacks.