After OnDemand upgrades, we sometimes have instances that appear normal (e.g. when viewing the dashboard) but give 404s when you go to view a particular page. The error is:

java.lang.NoClassDefFoundError: Could not initialize class com.atlassian.confluence.content.render.xhtml.StaxUtils

Our monitoring systems only check the dashboard (which returns a 200), so we do not detect this failure until the customer reports it. Restarting the instance will clear up the issue, but it's inconvenient for the customer as they need to contact Support about it first.

Temporary Work around: Disable the
com.atlassian.confluence.confluence-applinks-transformer-plugin