Many are using the redundant ESM (Primary ->Secondary). What version are you running? There were seval fixes in the 9.5.0 versions. I wold have support check to see if the secondary possibly has some detached partitions.
Are you also splitting the feeds between your ESMs? Or doing the HA sync? Do you also use ELMs and are they showing the same difference in events?
Ok, it has been solved with new patches on 9.5.2 version so right now our systems are total syncronized. These patches are included on 9.6 version.
It was a problem related to the files that the system send to syncronize.
ESM Redundant ESM: During ESM Redundancy runtime some events were missing causing the total events on the Primary ESM and Redundant ESM to be different. See KB87115 for more details.