When SharePoint goes bad: spurious error messages in the ULS logs that will lead you down a blind path. ULS logs were full of User Profile related errors, all saying moreorless this:
Exception occured while connecting to WCF endpoint: System.ServiceModel.Security.MessageSecurityException: An unsecured or incorrectly secured fault was received from the other party. See the inner FaultException for the fault code and detail. —> System.ServiceModel.FaultException: An error occurred when verifying security for the message
Spent a while looking through the UPS app config, Profile DB and everything looked normal. The issue is actually a “generic” WCF error – whereby the system clocks on the App Server (1) and WFE server (2) were out of sync by about 6 minutes. Manually setting the clock on the slow one to the current time resolved the issue.
Here for the full info.