Do you have more than one account? If so, the returns might be there. 

Also note that TRA (Tax return access) services were only available for paid TurboTax Online returns (including those with PLUS features added) before 2019. So, if you didn't pay for your 2017 or 2018 returns, they would not have been saved.

You can still get the information from your older tax returns via the Canada Revenue Agency (CRA) using their My Account service, which you can login to here: My Account for Individuals