I am having a similar problem. It happened when I first installed Spa Day. I was able to play for quite a while, then I decided, since I also have Get to Work, to have one of my sims get a job as a detective (another sims in the household is a scientist, but I wouldn't think that would make things go haywire, but you never know). When I sent her off for her first day as a detective, that's when the trouble started. Previously, I had sent my scientist sim to work and joined him, but for some reason the game must've not liked what happened with the detective. It took me to a loading screen and back to the town map. I clicked on my household and it said something like, "pick the sim you want to play". I picked one, and it took me to another loading screen and back to the world map. I kept trying to get back to my household, but I'm stuck in this infinite loop. I even tried other households, but nothing seems to want to load. I even tried deleting the detective sim (without saving afterwards) just in case there was some glitch in her, but that didn't work either. I'm hoping you could take a look at it, and see if you can tell what's going on?
https://www.dropbox.com/s/rrs3bcqm8pcnhah/saves.zip?dl=0
It'd be much appreciated! 🙂