Gen 7. I personally got a save that was game sync'd (which uses the value they are also assigning even to recent saves, despite no game sync feature in later games) softbanned. I accidentally had a region changing cheat on when going online, without realizing. They captured the info of the save, and the system automatically detected something that obviously shouldn't happen. (having 2 different regions between saves).
I can't give you a range of when it happened, simply because it's likely automatic detection that was working all year round once it had been implemented. Could no longer use that save for game sync purposes, so I had to wipe the value and get a new one.