I called support about a second BE550 unable to EasyMesh being faulty, but now I think it's an issue within the BE800 firmware. I bought a BE800 and a BE550, the BE550 essentially for a wireless bridge for a desktop that has weak wifi issues and its been stable (currently firmware 1.1.1). I bought a second BE550 to wireless bridge my AV stack with old WiFi devices over ethernet.

When I tried to add the second BE550 it took a couple tries before it joined, and since then the attached devices will lose Internet until the BE550 is rebooted. Tonight I tried another factory reset to see what would happen and no attempt to join EasyMesh was successful. It looked like the 2 BE550 were trying to daisy chain from the BE800 EasyMesh map, but they are on opposite sides of my apartment with the BE800 central.

I factory reset all 3 and this time joined the second "bad" BE550 first which was successful. This time the first "good" BE550 that has been stable is unable to successfully join EasyMesh second.