I recently ran into this issue myself and the most generic solution is to make a new merge / pull request to duplicate the decoration not working, then check the SonarQube logs and fix whatever it is complaining about. You can do this within your SonarQube instance from Administration > System > Download Logs and look for errors. I found the relevant errors in my case within ce.log
In my case the solution was to update the “repository name” field within the relevant SonarQube project’s “DevOps Platform Integration” section:
Sonarqube Project Settings > General Settings > DevOps Platform Integration > Repository Name.
Apparently for PR / MR decoration to work this field has to be correct + in the correct format which is the last part of the project URL that looks like organization/repoName.
On the “DevOps Platform Integration” page there’s also a button to “check configuration” that verifies if it should work with the current configuration. If this is green and you still have problems, there’s something else going on. Again- check the sonarqube logs as I described above.