jimmy1998, I was hoping to see a Jenkins stack trace. However, it is now clear that the problem is indeed in blueocean-bitbucket-pipeline and has to be fixed there.
So far, I don't see any such fix in https://github.com/jenkinsci/blueocean-plugin/pulls and I don't know whether anybody is working on it. (PR #2196 will not help; it upgrades the build-time cloudbees-bitbucket-branch-source dependency to 2.9.11, but if you have installed that version, then it is used at run time anyway, even without this PR.)
Until there is a fix, you can perhaps work around the issue by using the older Jenkins user interface instead of Blue Ocean.