Possible Solution:
I've been experiencing the same frustrations. Started a couple of weeks ago. Witnessed all of my weekly icloud appointments disappear before my eyes, but they remained on my iPhone and my iPad. I'm guessing this fix has already been posted somewhere, but here's what Applecare told me to do. It's worked, at least so far.
1. Delete icloud from your iPhone. (Settings - iCloud - Delete Account).
2. It will ask for a confirmation. Select Delete.
3. Very Important - It will then give you the option of keeping the information on your iPhone. Make sure you select this option.
4. Power off your iPhone and turn it back on.
5. Go back into Settings - iCloud, and re-create an iCloud account using the same Apple ID as the one associated with the calendar you're trying to fix.
6. Select the "Merge" option when prompted. This will merge your iPhone calendar with the iCloud. Make sure Calendars is set to the "on" position in iCloud Settings.
That's it. When I followed these instructions, I watched the missing appointments reappear in my iCloud. It wasn't perfect. For whatever reason it didn't merge my most recently added events from my iPhone during the last 24 hours or so. But relatively speaking, I can live with that.
Hope this helps.