The diagnostic heap dump endpoint /heapDump/ cannot be used to download heap dumps anymore because it does not meet the requirements of https://github.com/openjdk/jdk/commit/fb87831bf8ffccc27c4f42e72d0beac4ef38a741: The temp file has a hprof suffix, not .hprof, so does not pass this check.

This was introduced in:

https://www.oracle.com/java/technologies/javase/7u151-relnotes.html

https://www.oracle.com/java/technologies/javase/8u141-relnotes.html

https://www.oracle.com/java/technologies/javase/9-relnotes.html

A workaround would be to set the system property jdk.management.heapdump.allowAnyFileSuffix, which can be done while Jenkins is running, via the script console.