Help Please - Broker unable to return result set

We had to bounce all of our druid nodes today with this being the suspected error in the broker logs:

2019-03-20T19:24:56,173 ERROR [qtp2095225389-127[groupBy_[test-data]_f8a5cad6-1c6d-4e89-9207-6234910b9c34]] io.druid.server.QueryResource - Exception handling request: {class=io.druid.server.Query$ Failure getting results for query[f8a5cad6-1c6d-4e89-9207-6234910b9c34] url[] because of [org.jboss.netty.handler.timeout.ReadTimeoutException]

I will keep digging, but I didn’t find any root cause or related errors yet in the Overlord, Coordinator, Historical, or MiddleManager logs.

Any ideas?

After cycling Druid, everything worked fine again.

Could it have anything to do with the numthreads or connections settings on either the broker nodes or the historical nodes?