Events revert after changes made to cal event

Periodically, when changes are made to an event, the event will revert to previous version and changes are lost.  We are using Zulu via FM 15 server with multiple devices - 6 desktops (OS Yosemite10.10.5 & Sierra 10.12.2), 7 iPhones, 5 iPads.  Daily there are 15-25 events being added and modified throughout the day.  One example, user on iMac edits an existing event to add notes, clicks "apply" and when he goes back to the event, the notes he just added are gone.  This happens multiple times daily.  Another persistent issue is if a user on mobile device changes time of an event, the event will jump from the time the user selected to 3 hrs in the future.  (We have checked time zone settings on all devices already).  Also, when user on iMac changes event from one user's cal to another user's cal and/or changes the time, it will often revert back to previous user cal & time setting. We have brought this issue up to our FM programmer and I believe they contacted 360 Works but we have never gotten any resolution to this issue and it has been going on for months.  Anyone else experiencing this or have any input?