Homekit with Meross smart bulb

I successfully setup 2 Meros MSL120 bulbs with apple Home app, as well as a garage door opener. I'm trying to set up a new MSL120. The bulb successfully configures (flashes RGBw colors for successful configuration), and connects to my wifi 2.4 gHz network (the bulb and iPhone are in the router's wifi 2.4gHz list). But the Home app won't finish the integration with Home app. It doesn't move onto the app configuration (e.g. room and name designation). The app tries to connect for a minute or more, then states: Unable to connect, with an "unknown error". I've turned my router's 5gHz wifi off (Asus RT-AC88U). The other hardware/software: iPhone7, iOS14.6, 4 HomePods, and all apps are auto updated.

I've tried both bulbs in the box, and reset the bulbs in between each of my many attempts. I've also tried using my iPad Pro, same result. The iPhone & bulb are within 2 feet of each other, and within 5ft of router.

Any ideas?