This might be changes that have occurred with Siri. Assuming it’s the HomePod listening to your commands. One workaround without having to set everything up again would be to use Siri Shortcuts . Without knowing where it is you’re using the Homekit Home App it’s hard to advise. I use the Hue app on my iPad. There is however a shortcuts app to perform these tasks to make your own phrase to operate the lights.
If you’ve grouped the bulbs into one scene or room with Hue it’s going to operate both lights. I have 3 in my livingroom that I didn’t lump together, two lamps are together in “ livingroom” and one behind my TV I put in “TV Room” so my TV light doesn’t become part of my commands. Although I could add it in if I wanted to by not having that bulb change it’s brightness level.
It’s just easier to use the Hue App Scenes for what you’re trying to accomplish. It will take so practice learning how it works. For example you put both Bulbs into one room , then you start making scenes In that room . In one scene you are just wanting the one bulb to come on at a desired brightness so let’s say you set that bulb to 80% and you set the other bulb to 0%, so only one bulb will brighten to its desired level using the command you gave it. You can use the Hue App scene’s edit button to record a shortcut phrase which might be “ turn livingroom lights on” and it will come on with one at 80% and the other not brightening at all ( Off). If you have times you want them both on, all you have to say is “set livingroom lights to 80%”.
it’s hard to explain. Took me awhile to get mine working how I like them.