Can you please tell us steps to reproduce this?
I'm sure you must have fixed this by now but answering so that others can fix this.
I had been facing this problem whenever I was trying to publish a page along with a NullPointerException in the logs . On further digging, I found that AEM tries to find references for the page, including the configurations inside /etc/cloudservices (and I'm sure there could be more).
In my case, a jcr:content node was missing under one of the configurations which was leading to the NPE and the "Failed to retrieve references.." error. I simply copied a jcr:content node from other configs and removed the unnecessary properties, except the sling:resourceType property and was able to fix the error.
at com.day.cq.wcm.webservicesupport.impl.ConfigurationReferenceProvider.findReferences(Confi gurationReferenceProvider.java:86)
at com.day.cq.wcm.core.impl.reference.ActivationReferenceSearchServlet.doGet(ActivationRefer enceSearchServlet.java:115)
at org.apache.sling.api.servlets.SlingSafeMethodsServlet.mayService(SlingSafeMethodsServlet. java:269)
at org.apache.sling.api.servlets.SlingSafeMethodsServlet.service(SlingSafeMethodsServlet.jav a:345)
at org.apache.sling.api.servlets.SlingSafeMethodsServlet.service(SlingSafeMethodsServlet.jav a:376)