Starting with version 1.31.5 my team now sees a "WARNING" in "jenkins.log" for every build agent/"slave" that connects. This was introduced with the deprecation of "JavaVersionChecker", pull-request #203
It seems the warning is produced for every failed guess on the Java binary that is not just 'java' (the "PATH" possibility). As noted in the comments for issue #43779, the order of "resolution" of Java version implies that guesses are made in a particular order.
In my team's case the agents are set up with the desired Java version in their "PATH" and because of this we now see this warning. I believe it is an error to produce this warning when a guessed Java binary is not the actual Java binary on a particular system. As long as Java is successfully resolved, why produce a warning?