If you EVER going to make a Jenkins Shared Library with src/com/whatever packages and classes. NEVER make them .java...
It utterly breaks anything with importing for the global shared library and the files are simple not added to the Lib folder for the job.
Use .groovy.
Think I'll be writing an article on this later as I simple cannot find a clear answer on this anywhere on this; and generally how to support multi class hierarchies.