Had the same issue with a slightly different circumstance and thought I’d share in case someone else is having the same problem. So when I added 4 new BR30 bulbs it prompted me to create a group which I did. When attempting to use the group I would get the same firmware message and not be able to do anything.
The way to resolve it, is to delete the group, then proceed with what others stated (turn off lights via app not switch) and then proceed to hit the update now when prompted for firmware update.
Couple of times of notes for engineering team working on app … when selecting Update all at once, either with or without a group, the bulbs do NOT appear in the list of hardware items to update. You MUST choose the update now option in each individual bulb when prompted.