Thanks for the logs,
Since you’re using GitHub Action, do you use this one: SonarCloud Scan · Actions · GitHub Marketplace · GitHub ?
This GitHub Action doesn’t work with Dart properly, because it doesn’t have access to the dependencies, so it’s better to use a workaround mentioned here: Dart: support Melos dependency management? - #7 by Margarita_Nedzelska
And the tutorials for Dart has been updated.
It would also help if you looked at the reported issues and told us if you saw anything strange. Usually, you should see messages with an Invalid primary location reported as S2260. Make sure that the rule is activated and check again.