Hi @KristineKey
Like @TrishaMeyer1 mentioned, it would be good to have some more information regarding your situation. Ultimately it also depends on whether or not your grade sync is managed by Canvas or not. You can always reach out to Canvas Support to have them look over your set up.
I know from experience that assignments without a due date will not sync. If you have more than one assignment with the same exact name, there are integrations that will not allow either one to sync. Bottom line though is that either submitting a ticket to support or posting some screen shots of your assignments list in Canvas (indicate one that isn't giving the option to sync) as well as the grade sync interface showing that it is missing is what needs to be done. Be sure to also let us know what SIS your school or district is using.