Can you give more specifics about your environment and scenario? Unfortunately what you've provided leaves us flying blind.
Let's start with environment: what version of Exchange Server, what version of Outlook on desktops, and what OS?
Are they making modifications to items in their calendars, shared calendars, or meetings?
Are they doing this via mobile, web, desktop, or all?
I haven't experienced this myself or heard of end users experiencing the same, but let's see what you come back with and we can work from there.