Hi Janos,
It was indeed HEAD of the PR mismatch. While the pipeline itself does not do anything special with git checkout, the Jenkins job configuration did, by applying strategy: Both the current pull request revision and the pull request merged with the current target branch revision which resulted in new sha1 which did not exist on the remote side.
Switching to The current pull request revision strategy fixed the issue and SonarCloud Analysis PR check is set as expected.
Thank you