Time for an update with this whole saga.
After my call on Thursday night, I added Power Bar 2 back in and slowly added equipment back on it. Heater, Mitras light, ATS lights, and then return pump. This was done over 2 days as time allowed. I had to give enough time in between each addition to see if I eventually got a notification. Happy to report not a single problem.
In the meantime, I had Power Bar 1 plugged in in a separate room but nothing plugged into it. I added PB1 to the power strip that PB2 is plugged into. Got a notification for both Power Bars that they weren't responding. 30 minutes later both sent a notification saying everything was fine. It was a quick glitch and nothing shut off in the process. 6 hours later and no other notifications or issues.
I will now start adding the three remaining pieces to PB1. They are a Tunze 6045, ATS Sicce pump, and Reefbreeders ATO. We'll see if anything interrupts the system and causes problems again. I'm also getting a multimeter to check for stray voltage.