Ideas
I am having this same issue. My sim was offered a chance to do the Love Highland Getaway. I took it, and at first, everything was fine—he was able to flirt and interact with another sim. It was bedtime, so everyone else just went to bed as expected. Eventually, I sent my sim to bed too. Everything was fine until the morning. Instead of getting breakfast or talking or even moving, all the sims just stood by their beds, frozen and not moving, including my sim. I tried resetting him and sending him to the bathroom, but he just stood by the toilet while his needs dropped. After two hours (in-game), I gave up and cancelled the getaway.
My save file isn't huge: 28 MB. I do have residential rentals, but not an overwhelming amount, only 13 total for the whole game, and over half of them are just shells. My lots are not overstuffed. Willow Creek, Magnolia Promenade, Tomarang, and Sulani are completely blank. I have been porting my sims and builds over to this save fresh, so it's only a few months old. I'm playing on a relatively new Gaming PC, and my specs are well above the minimum for the game:
Processor: Intel(R) Core(TM) i7-14700K (3.40 GHz)
RAM: 32.0 GB
GPU: NVIDIA GeForce RTX 3060
This issue has only become a problem for me since the last update (12/2). Before that, Getaways worked fine. Well, not fine. I had all the normal bugs with sims doing odd things and the occasional role not showing up, but they were functional.