I recently upgraded a server from 11.0.0 to 11.0.1. One of the apps utilized my DAO bean I created a while back which was able to automatically manage to access the underlaying database depending on if it runs on premises or on IBM Bluemix (now known as IBM Cloud).
After the upgrade this app threw errors that some Java classes are unknown.
javax.servlet.ServletException: java.lang.NoClassDefFoundError: com/ibm/xsp/bluemix/util/context/BluemixContextManager
Those classes are the Bluemix classes introduced a while back.
If you are going to upgrade to Domino 11.0.1 you should check your apps if they are using those classes. Once I removed the references and switched to the simple usage of "current database" on all of the Xpages and Custom Controls, the app continued to work again.
This step totally makes sense though the removal happened without any warning - at least I was not aware of this. If I missed the technote about the removal, please feel free to drop me a note to it.