Session token error

We are trying to upgrade from 2.6 --> 2.8 - When we do this we are getting session token issues. It appears to be in the cloud function users/me. We orginaly thought we may have code that is loading querys storing objects and not using a session key or master key - we went through our code based and cleaned this. We still get the issue. If we roll back to 2.6 the issue stops.