There 2 problems that's comes with this:

PR's to a branch without Jenkinsfile but working branch has a Jenkinsfile are not executed by jenkins.

ERROR: /var/lib/jenkins/workspace/<organision>_<repository>_PR-15-QN42E7GZF23RNDD3R6SOUQOVTDJI2IGDB4C7LFJ5M35IGM43I4XQ@script/Jenkinsfile not found

PR's where a change has been made in the Jenkins file are still executing Jenkinsfile of origin branch.