Suddenly, finding lights is spotty

I’m a long time user with dozens of hue lights and devices on my hub. Suddently, it seems, adding lights is impossible. I’ve tried search /retry, serial numbers, power off / disconnect from network the hub to no avail. In addition, two existing lights I am able to control using HomeKit do are not even listed in the Hue app.

I primarily use Homekit, but it’s not possible to add a light using Homekit (is it?) and in the meantime I have five new bulbs that I can’t add, and two which are invisible to Hue.

Can anyone (you will pardon the expression) shed any light on this?

I do not want to factory reset — I have way too many lights on my system.