I just started having this issue today, and it's a dealbreaker for me with the Sims. I can't believe you've been experiencing it since the September update! I've never had mods or CC. I'm on a PC. To be extra careful, I completely uninstalled and re-installed The Sims 4, and then I started a new save file. It took 20 minutes (and multiple successful loads) but it happened again: the infinite loading screen, specifically when returning to the home lot. In the first save that kept sticking here it would also happen when trying to play the lot from Manage Worlds (build mode worked, but play didn't). Could it be an Island Living problem? Fishing is still not working there, either, but it does in other worlds.
We can't play the game like this! Help!