Hi,
Welcome to the community!
You said that your branch is baselined against main. Is it also rebased?
Is this ticket (fixed in 9.1) relevant?
SONAR-14929 - New Code using a ‘reference branch’ doesn’t detect changed code with git merge workflow
Is this one (expected in 9.3)?
SONAR-15697 - New code detection when using reference branch and rebasing doesn’t detect some commits on branch
Ann