Not sure if this applies to you. Please only use the link in the email about tracker account sent to you to create an account, if you have received it. It seems that IRCC has different "Tracker" system for different types of applications. My family has a different application (not citizenship) and I thought I can just create an account on the same webpage, but that system didn't recognize my UCI and application#. Then I clicked the link directly from the email I received about creating tracker account, then it worked!