I had this issue when I deleted an iOS app from my Firebase project and created a new one. The AASA (apple-app-site-association) file was showing both the old and the new app listings and this caused my dynamic links to be broken. I reached out to Firebase support and this was their answer:
Just an overview, your AASA file is tied with your project’s OAuth Client IDs. These OAuth Client IDs are created when an app is added to a project and not necessarily deleted when you delete or edit your app on the Firebase dashboard, and can consequently cause issues with the AASA's app listing. If this is the case and you have deleted or modified this app before the issue occur, you'll need to manually delete the associated OAuth Client ID/s in the Google Cloud Console in order for it to be removed in your AASA file. You can do this by following the steps below:
- Go to the API Manager.
- Select your project.
- Delete the OAuth 2.0 Client ID for the incorrect Bundle ID
- Allow for an hour to pass and check your AASA to see if it has updated.
This worked for me!