Customer reported a strange UI when running spark application through Oozie in Uber mode (Issue was observed only in yarn-client mode).
When debugging the sparkUI through chrome developer console, figured out that CSS files are looked for in different applicationId (Oozie mapreduce application) instead of actual spark application. (Please see the attached screenshot for more information).
Looking into the live sparkUI code, it seems that proxyBase is taken from APPLICATION_WEB_PROXY_BASE instead of spark property spark.ui.proxyBase (Pointing to the actual spark application). This issue might be reproducible if the above specified env is set manually or set by other job.
Fix would be giving precedence to spark property (which might be correct in most cases when it was set).