I have just installed Vassal 3.2.17-linux
I am on an Ubuntu 18.04.4 LTS laptop
I launched from the terminal, this is the warning I get. The program seems to be running fine.
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by VASSAL.tools.image.ImageIOImageLoader (file:/home/username/Vassal/lib/Vengine.jar) to field sun.java2d.cmm.ProfileDeferralMgr.deferring
WARNING: Please consider reporting this to the maintainers of VASSAL.tools.image.ImageIOImageLoader
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