After upgrading to 9.0.4 from 8.2.x, Splunk Web loads with a blank page, just the Splunk logo.
Upon researching this issue, we found a couple of users reported exactly the same behavior, and it was found that re-naming $SPLUNK_HOME/etc/apps/search/local/data/ui/views/search.xml to seacrh.xml.bak then restarting Splunk resolved it for them.