Ok I see what happened - and this is a bug. I've just gone through a full season using debug mode and there is a critical moment where if you hit the wrong button you get sent back to the career loading page and miss out on the contracts page. At the end of the season, when it shows the final results, you scroll to the bottom of the page and have 2 buttons, Return to Career or View All Series - if you click on Return to Career (left button), you get punted back to the load career screen and that's where you miss out on contracts and the next season starts with no change and no way to go back at all. If you click on the View all series button, this is where you can go through to the contracts screen.
If you miss the contracts screen like I have in my main career it breaks the entire career and season files are no longer generated, and you have no way to go back to the contracts screen you missed.