Hello @Craig-C  Greetings from Cloudera Community. Based on the Post, Spark UI is available for Running Jobs yet the Spark UI isn't available for Completed Jobs.  Note that Spark UI for Running Jobs is Serviced via Driver yet the Spark UI for Completed Jobs is Serviced via Spark-History-Server. We have observed few Scenarios wherein Spark UI isn't available for Completed Jobs during High-Concurrency & have a Solution until a Long-Term Fix at CDE. The Solution is a bit Verbose & as such, We shall recommend your Team to file a Support Case with Cloudera Support & We shall help your Team confirming the Issue reported above while applying the Mitigation Solution until a Long-Term Fix.  Regards, Smarak ... View more