I had a guy working in a customers house ask me about his Eero system at home. He described the exact same symptoms. He claimed he called Eero multiple times, and they finally admitted there was in issue with some iOS devices connecting - take it for what you will.

I've deployed maybe 4-5 Eero systems and they've all worked fine. I do have one that's dogging me. It's comprised of an Eero Pro 3 access point system. Two of the access points are hard wired, and one is wireless. The wireless unit is about 30 feet away from the one of the wired units, on the second floor. Even though it shows great signal, when an iOS device jumps to the wireless unit, it sometimes loses internet from some reason - it's sporadic as well - of course this issue crops up after I leave.