I have seen this twice before. The first time I don't remember, the second
time was this afternoon.
Not the error_log messages. But we had a situation this afternoon when the
server suddenly did not respond anymore. The httpd job was running. No
messages there. No messages in the error_log
I looked with glance and there was no httpd processes doing anything !!!
I restarted the job and everything was normal again.

Peter