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This appears to be an instance of a fairly notorious problem where apps exhaust the entropy of a system, expressed as availability of bytes from /dev/random.The Java developers were clearly aware of this problem (read , which per the Javadocs for NativePRNG.java), is the "default seed source".
I'm not convinced though, because my threads don't contain a FileInputStream.readBytes(), but presumably kept call, as would be the case if /dev/[u]random as "the default seed source" for backwards-compatibliitywas really being read, as shown in this example of /dev/random blocking in Bamboo. If anyone has suggestions, please comment.
The fix
Stackoverflow to the rescue. Per the advice there for Java 11, I now set:
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