i dint understand the issue completely - i would ask you to provide more indetails about it.
"users that are seeing other users meetings/appointments even though they are not invited or a part of it."
based on the above description what i understood is few users able to see other users calender/meetinv invites
are the users are using any MDM software which is your company provided if yes check the MDM software functionality.
if not, check any calendar sharing permissions are creating any issues with it.
Regards, Rajukb | MCSE (Communication ), MCSA (o365) ,Certified "Lync server 2013 depth support engineer"| This posting is providedwith no warranties and confers no rights. If my reply answers your question please mark as answer/helpful if its
helpful.