Do you see video artefacts on your MacBook Pro when opening the Java control panel? Calling all MacBook Pro 15" 2018 owners, particularly owners of the 2.6 GHz model. Would you be willing to test something on your 2018 MBP? (15”?). Install the latest Java JRE (https://download.oracle.com/otn-pub/java/jdk/8u192-b12/750e1c8617c5452694857ad95c3ee230/jre-8u192-macosx-x64.dmg).
I see weird video artefacts every time when I do this: 



The test needs to be performed without an external display attached as it appears to involve the discrete GPU.

I need to figure out whether my MBP 2018 needs a repair before I leave the country on Tuesday … The issue isn’t permanent, by the way! If you relaunch the Finder, it goes away.

I'm running OSX Mojave 10.14.2.
It turns out that the integrated GPU was defective.