Graylog 3.1 upgrade failed to start with standard v3.1 plugins

[JHilke (Joel)]

Glad this post has helped some others.

I have another post that I need help with, as this was a different system upgrade:

Graylog Content Packs page will not load after upgrading from v3.0 to v3.1

We just upgraded our test Graylog 3.0 server to v3.1. Afterwards, I noticed the Content Packs link on web page would hang at “Loading…” The below message appears in Graylog server.log 2019-08-20T17:01:57.051-04:00 ERROR [AnyExceptionClassMapper] Unhandled exception in REST resource java.lang.RuntimeException: IOException encountered while reading from a byte array input stream at org.mongojack.internal.stream.JacksonDBDecoder.decode(JacksonDBDecoder.java:67) ~[graylog.jar…