On my computer, my user became corrupted. I had no idea that was a thing, but it is. Once I figured out how to create a new one and grant it admin status, I had to copy EVERYTHING over to the new user. All I had to do to get into TS4 again after that, was to log into Origin as if I were on a different device. All saves, CC, mods, etc. were fine after that.
I've just discovered I've got a much bigger problem with my flight simulator, FSX Steam Edition. It forgot ALL of my settings. I've got a yoke, pedals, and 2 throttle quadrants linked together, and had a lot of keys and buttons customized over quite a long period. That's going to take me a while getting it all back the way I want it.