Then, I blocked all executables from 'The Sims 4' folder (inside Program Files x86) on my firewall. Then, I tried the game again, same error. Well, I clicked OK, left the game WITHOUT saving and closed everything. It's funny it happened even though I am playing 'off line' and without Origin at all.
I also noted that, even if the game says it's not connected (I know about the trick using a fake origin account, but I didn't do anything related, since I am just trying the basics), today I got a notice that the 'server would be down in 10 minutes', which would change, in a few seconds, to 5 minutes and to 'down now'. Note that I do NOT even have origin installed on my computer (I also checked the task manager, just in case). Today I was going to play again, with that save, and I get the 'Game Data Incomplete' error as below: I played a bit around, recorded a few videos, saved everything and closed the game. I had my first saved game last Friday, for which I have videos on this topic.