Hi Poonam - We had a similar issue recently in our environment in an attempted upgrade to 9.1. We found that there was a reference to a System Property called: mxe.useradmin, which was undefined in our system (with an Oracle back-end). With this missing System Property, the MASUSERSYNC Cron Task would run and do nothing. We went ahead and updated the value, like this:
UPDATE maxpropvalue SET propvalue = 'maxadmin' WHERE propname = 'mxe.useradmin';
After we re-ran the MASUSERSYNC Cron Task, we found that our users had synced over to Core.
Hopefully this work for your as well.
Aaron Paroulek
Maven Asset Management