Somehow you gave me the idea to copy my laptop’s “PythonMode/” folder to my desktop PC. 
And it just worked after that! 
Seems like even though PDE’s Contribution Manager says it’s gonna download Python Mode build 3049, it actually downloads build 3050! 
Just checked that build 3050’s “PythonMode.jar” file was compiled by Java 11. 
AFAIK, Java 11 is still incompatible w/ current PDE! Needs to be at most Java 8. 