Sonarcloud is analyzing very old pull requests. example. This is getting noticed because the summary is posted as comment.
This is an annoyance, because people get pinged for it.
You’re not using automatic analysis, so this is a question of what GitHub Actions is being prompted to act on. That said, it seems there was a new commit on the underlying branch on Dec. 5th. It still seems odd to me that that was only processed 4d ago, according to SonarCloud. But the analysis doesn’t seem random.