I let Windows update me to Windows 10 Home 1803. A side effect of this is that it deleted the PreferExternalManifest registry key that is part of the solution for running Java on HI DPI systems. I restored the key but neither Java nor any of the other apps that used an external manifest worked as expected. I had been running Java 8 and the ever reliable internet was claiming the issues really were fixed in newer versions. Java 9 is no longer an "I don't want an Oracle account" download so I sucked it up and went to Java 10. My HI DPI problems seem to have been solved and neither Windows nor Java 10 required any additional configuration on my part.

For the record a non-Java app worked without an external manifest after changing the Compatibility properties.

If it comes up again I'm going to suggest people upgrade to Java 10 OR not upgrade to Windows 10 1803.