Hi @Darnellcotez I've play tested this for hours and I haven't been able to find out why it affects some Sims and not others. Obviously the devs have tweaked the autonomy/fun gain levels, hopefully they'll have figured out a fix SOON!
Resetting the lot as per @PeopleMatterMore solution works, but I found that I had to replace the beds because they are automatically claimed, and in my game that borks the energy buttons. But after resetting the lot the fun button did work for one of the three adults in my household, the other two I think have stressful characteristics, for example one is ambitious, and the other is a game designer and suffers a lot of stress during work.
It might have been wise at the beginning of this thread to list the traits and aspirations, age, employment etc of the affected Sims, maybe we could have found a common cause as it's simple enough to change their personalities in CAS.
edit: don't waste your time on the above! I've got a stack of paper in front of me with lists of traits and aspirations etc, and I can't find common ground in any of it.
Still I have one adult male that autonomously fills his needs and all the auto solve buttons work.
One young adult female who cannot do anything autonomously any more and stands outside at the front of the house for hours! The auto solve buttons for hunger directs her to the ice cream maker, energy to the coffee machine, and social to trolling the forums - all of which raise her fun levels.
And one adult female who can fix her needs autonomously, though it rarely happens quickly and she seems to spend a lot of time idle. All her auto solve buttons apart from fun work normally.
The other two family members are a teenage and a child sons, they seem to be able to find their own fun. But the teen boy's auto solve fun button doesn't work.
It's not completely the game breaker I was moaning about in the first place, it's most definitely improved since following @PeopleMatterMore suggestion, but the fact remains it's broken, and most likely that's because the devs have tweaked the settings in preparation for some future content and that's just wrong! Why not hold off with the fiddling until they're ready to release what ever it is they've got planned?