There's a distinct sign-in page for each tax year of the online editions of TurboTax. Is it possible you signed in to TurboTax for tax year 2017 and then later signed into TurboTax for tax year 2018 expecting to see those 2017 returns?
Here are a couple of our FAQs you might find helpful...
How to track down TurboTax returns if you're having trouble:
And how to delete returns: