Hello,
I have had this happen twice in the last week, once on two different save files set up exactly the same. The save files were test runs for a particular challenge. The first test run file has been deleted, but I still have the second one. I'll give as many details as possible in hopes it will help give the devs a clue as to why this problem keeps occuring to others. First, let me say I've never had this problem before because I normally play with aging off and age up my Sims using a cake if necessary. In saves where aging is on, for example a legacy, the cake always works and all buttons are still fully functional afterwards.
Set up:
Aging on for households and all other Sims, short lifespan, full autonomy, one young adult male Sim. I have no mods, no CC and never have had any in my game.
EPs, GPs, SPs:
Get to Work, Get Together, Outdoor Retreat, Spa Day, Dine Out, Vintage Glamour, Romantic Garden, Movie Hangout, Spooky, Cool Kitchen, Perfect Patio, Luxury Party, and Holiday
Gameplay:
My Sims in both saves were located in Newcrest on the 20x15 lot named Comfy Cubby. In the first save he had a normal home with walls, but spent 99% of his time outside crafting objects on the woodworking bench. In the second save he had no walls with all objects in the open air, still spent 99% of his time crafting objects on the woodworking bench.
In both saves, when it came time for him to age up to Adult, I let it happen naturally without a cake and he was working on the woodworking bench when it happened. No other Sims on the lot, just him. I suppose others could have been walking by his lot or in the area though. I didn't notice.
After he aged up, I could not save, go to build mode, go to manage worlds, nothing. These buttons were grayed out and when I clicked on them it said, "Can not do this action while a Sim is aging up." He had already aged up. I sat there a moment wondering what to do and then finally just sent him to sleep. While he was sleeping the buttons became active again after a Sim hour. I saved the file each time and exited the game.
Also, I don't know if it matters but thought I should mention that my Sim was in and out of build mode a lot in order to sell objects he had crafted. I also paused a lot. I never used the third speed button myself, it was only in use while he slept. In both saves he also waited until the power was turned off to pay his bills, twice. In each save he had a relationship with only one Sim and never called any NPCs to his lot for services. Both Sims in the two saves also upgraded 15 times on objects located on his lot. Both Sims in the individual save files also fulfilled a lot of whims and purchased the Marketable reward trait with satisfaction points.
Lastly, each save file had a mathmatical drawing crafted on an easel by the fountain next to the library lot in Windenburg which he brought home via inventory and hung above the woodworking bench. This is probably tl;dr information, but perhaps it'll help.
Thank you for looking into this matter and I can provide the second save file if necessary. Just let me know. 🙂