I have 100 ppl all at 100% happiness and a not active radio station. I took the DJ's out and rushed every person in every room to 100% but in still at 99% over all. What am I missing?

I have the same issue. I have all 136 dwellers at 100%. Yet it only shows 99%. On the daily evaluation it gives me 100%. My guess is that there must be a dweller or two somewhere that are a fraction below 100%. Like 99.7%. So essentially it shows dweller at 100% rounded up, but overall happiness in not a true 100%. Other then that, a bug maybe?

Remove your radio station, rush everyone's happiness up again (like if they had 99%) and see what happens!

This fixed it for me. Now my vault's happiness shows as 100%

Did that. And still 99%. Still getting 100% on evaluation. But in game screen still shows 99%

Are you 100% sure that you reworked everyone's happiness? Even counting explorers and people assigned to rooms where you can't sprint? I know it's not easy, expecially when individual happiness shows as 100%.

Do this: rebuild your radio station. Assign high charisma people to it, then, after a while, remove them from the station and demolish it again. Now, individual happiness shouldn't show as 100% anymore, making it easier for you to see who needs to be more happy

My dudes are often less happy than I'd like. So, I sort on Happiness take the lowest ranking people and make them explore the Wilderness without stims, weapons or armor . When they die, overall Happiness goes up

I think it's a bug actually. Often you get the objective "raise [x] amount of dwellers to 100% happiness", and there's a bunch of 99% happiness dwellers in my vault. I promote one to be a DJ (gotta play them funky tunes), and suddenly the objective said it's completed. The happiness for the dwellers however hasn't changed in my overview screen.

I found it's just a lot easier to keep the happiness above 92% and not bother with it otherwise, saves a lot of stress.