This was resolved by applying Patch #170489. Events resumed entering the log again.
Hello All:  I have a 21-node Isilon NL400 Cluster running OneFS 8 (8.0.0.037), joined to an AD domain. All new events on the cluster (except for Heartbeats) have stopped entered the 'Event Groups' log.  An 'isi status' indicates that the cluster is green, and all the nodes are green even though there are nodes that obviously need attention.  As workarounds:  I can generate an isi_gather log and evaluate the cluster's health with the Isilon Advisor tool. The actionable issues appear red and orange as expected. I can also manually examine individual node issues (i.e. drives that have Smartfailed, etc.), in the cli and gui.  The 'Event Retention Settings' are set to their defaults (90-days, 1MB per TB).   Thanks in Advance.
Isilon OneFS 8.0 - New events have stopped entering the log