Having this same continuously building issue. We are using origin/master. I believe it has something to do with the @Library usage. 2 scenarios:
1) Pipeline being continuously triggered on every polling window. I edited the pipeline being run to remove the import of the library, and do nothing except print what stage it was in. Continuous looping stopped at that point. When I deleted the dummy build, the continuous building started again.
2) Pipeline being continuously triggered on every polling window. I deleted from origin all branches (except master), and closed all open PR's on the Global library repo. Continuous looping stopped.
We have tried all of the options in the configured Global Pipeline Library being used as well as all the options within the Pipeline script from SCM cloning options.
Jenkins - 2.107.3
Git plugin - 3.9.1
Pipeline SCM step plugin - 2.6