I tested the v2.1 plugin with the normal jenkins pipeline and all works fine, when it comes to multi-branch pipeline job, i can see in Bitbucket server it push the webhook to jenkins successfully on any code push, and in jenkins multi branch project log i can see logs like below:

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[Tue Sep 29 15:27:37 BST 2020] Received com.atlassian.bitbucket.jenkins.internal.trigger.BitbucketWebhookConsumer$BitbucketSCMHeadEvent UPDATED event from bitbucket-auto-trigger-test with timestamp Tue Sep 29 15:27:37 BST 2020
Found match against /folder1/job1
Found match against /folder1/job2
Found match against /folder2/job3
Found match against /folder2/job4
......
Found match against /folder3/jobN

 
but it is very slow, looks like it is searching the whole jenkins instance's multi-branch pipeline jobs to do broadcast on the branch event and it stuck at some jobs, when i remove the problematic job it goes further but stuck at some other jobs again. I am wonder whether this is something handled by the Bitbucket Server Integration plugin or it is with multi-branch pipeline plugin.  If i put my test job into the folder it scans first, e.g. folder1, it works fine.  Can you please advise?