I checked our bundle (inside /system/console/bundles) and it is running.
I stopped/started the bundle but it made no difference.
I compared error.log and our project log (before and after reinstalling the custom package) and nothing obvious is showing up there.
i tried Java 8 versions 202, 271 and 281.
I tried Java 11 version 8. Our AMS-provided 6.5 upgrade sandbox is using Java 11 version 5 but versions 7 and below are not available (404 error) on the Oracle website.
The workaround is to reinstall our custom code package and it will start working again.
Any ideas on where to look or how to fix permanently instead of having to reinstall our custom package every restart?