This has been happening for quite a while - my guess is since iOS 9 came out (before I got my Apple Watch last December) - it just took a long time to identify what was causing the problem because I don't always snooze/dismiss meeting reminders from my phone/watch. Also happens on Apple Watch if I just go to the notifications area, press long enough to get and use the clear-all option.

Same issue whether I snooze or dismiss from iPhone or Apple Watch. Has happened when we were using Exchange servers and later when we moved to Office365 servers, no change. I do not include myself in the invitee list. This only occurs with meetings I have scheduled and invited others to. When using my built in iPhone calendar app with my work calendar (based in office365 server and previously Exchange), anytime a meeting reminder pops up for a meeting which I scheduled and invited others to, if I hit snooze or dismiss on my iPhone or Apple Watch, Office365/Exchange immediately sends out a cancellation of that one specific meeting occurance (regardless if original meeting was a single meeting or recurring meeting) to all the invitees and sends out a new invitation to the same invitees for the same meeting session but without any of the text previously in the original email (details/notes about why we are having the meeting).