The / partition on jobrunner01 alerted for being 96% full. The /var/log/mediawiki/jobrunner.log file was 1.2G of errors.
2016-02-13T05:26:07+0000: Runner loop 0 process in slot 3 gave status '0':
curl -XPOST -s -a 'http://127.0.0.1:9005/rpc/RunJobs.php?wiki=ptwikibooks&type=htmlCacheUpdate&maxtime=30&maxmem=300M'
<!DOCTYPE html>
<html lang="en" dir="ltr">
<head>
<title>No wiki found</title>
...
2016-02-13T05:26:07+0000: Runner loop 1 process in slot 0 gave status '0':
curl -XPOST -s -a 'http://127.0.0.1:9005/rpc/RunJobs.php?wiki=commonswiki&type=gwtoolsetGWTFileBackendCleanupJob&maxtime=60&maxmem=300M'
...
<title>Wikimedia Error</title>
...
2016-02-13T05:26:07+0000: Runner loop 4 process in slot 0 gave status '0':
curl -XPOST -s -a 'http://127.0.0.1:9005/rpc/RunJobs.php?wiki=commonswiki&type=AssembleUploadChunks&maxtime=60&maxmem=300M'
...
<title>Wikimedia Error</title>Root errors seem to be "PHP fatal error: Class undefined: GWToolset\Config"