There is no buildMap rule we are using, though we are using creation/Customisation and mergeMap rule but we have not user org.jaxen in any of the rules explicitly.
Please check if you have multi version file at lib folder. WEB-INF/lib
try to download new ojdbc(ojdbc8.jar and ojdbc11.jar) driver check whether that makes any difference
Copy the downloaded jar file into this WEB-INF/lib directory.
The issue was that i was using Dom4J liberary to create an xmlPayLoad in my customiation rule, which internally uses Jaxen library to create xPath. In 8.4 Jaxen liberary is removed as it is no longer being used by IdentityIQ core code as per Support team, causing the error.
I fixed it by replacing Dom4j with standared java library such as javax.xml.parsers.DocumentBuilder, org.w3c.dom.Document, and javax.xml.transform.