On start of a slave using openJDK jdk-11.0.9.1+1 on slaves and master I get in the log:

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<===[JENKINS REMOTING CAPACITY]===>channel started
Remoting version: 4.5
This is a Unix agent
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by jenkins.slaves.StandardOutputSwapper$ChannelSwapper to constructor java.io.FileDescriptor(int)
WARNING: Please consider reporting this to the maintainers of jenkins.slaves.StandardOutputSwapper$ChannelSwapper
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
Evacuated stdout
[StartupTrigger] - Scanning jobs for node ullteb106

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The bold warning makes me a little bit nervous....

All these warnings are not present, if I use openJDK jdk8u275-b01 instead. (Everything else unchanged)

There is a similar report referring to Windows and (Sun) JDK9: https://issues.jenkins.io/browse/JENKINS-46631
And on JDK11, but referring to "after installing the selenium plugin" https://issues.jenkins.io/browse/JENKINS-64831

(We DON'T have this plugin installed)

I'm running Jenkins with JDK11, because in my understanding the switch is pending; I'm using openJDK because Sun/Oracle would need a license in my understanding.