P4_plugin will  not detect new streams in a multiBranch Scan if the Jenkinsfile`s change action is branch.  Once the file is edited once (thus changing the action to edit) the multibranch scan that will be run next will succeed in finding the new stream and add it's config.

Since we have a highly uniform environment based on conventions edition of the Jenkinsfile for development branch from a mainline is rarely necessary.  99% of the time programmers will only create the stream and work on their things without needing to touch the Jenkins file at all.

for example, the scan multibranch pipeline log returns this

 p4 files -e //proj/demos/2019.2/Jenkinsfile //proj/demos/2019.2/Jenkinsfile - no such file(s).
‘Jenkinsfile’ not found

while running the very same command line locally will yield :

p4 files -e //proj/demos/2019.2/Jenkinsfile
//proj/demos/2019.2/Jenkinsfile#1 - branch change 2190857 (text)
 

editing the file with a bogus change yields this locally :

> p4 files -e //proj/demos/2019.2/Jenkinsfile
//proj/demos/2019.2/Jenkinsfile#2 - edit change 2191573 (text)

and running the scan multibranch manually yields this log

p4 files -e //proj/demos/2019.2/Jenkinsfile 

p4 files -e //proj/demos/2019.2/Jenkinsfile //proj/demos/2019.2/Jenkinsfile#2 - edit change 2191573 (text) ‘Jenkinsfile’ found 

 
 
and the stream is detected and a build properly scheduled.