Very similar problem here I think, stuff not syncing correctly in any case:
I had this problem I just discovered about three weeks ago. Our family's iCloud calendars were not syncing. In particular my daughter's periodically would not sync when she was away at school even though her events were showing up on my phone and calendar anyway. It would randomly not work and there is no rhyme or reason why. It kept telling me I needed her password even though nothing had changed. So I can't tell if I am missing appointments or not.
About three weeks ago I realized that I was missing an appointment I put in a few days prior, which I was sure put in on my macbook and still didn't show up anywhere (phone or macbook) so I checked for it and couldn't find it. I added it (again?) on my macbook and a day later it still wasn't on my phone. Also a bunch of days for this month had NO appointments whatsoever between the four of us showing up even though all calendars appeared to be syncing (no error messages, no status alert icons associated with any calendar). Then went to the individual DAY on my phone and there was the mysteriously vanished appointment. When I viewed the individual DAY with the list of activities and scrolled forward to see my upcoming appointments, then they started to show up on the month view as dots on the days when I had appointments. They had not been there yesterday or this morning until I viewed the list of upcoming activities. VERY STRANGE because I did not change a thing.
Thank you, apple, I missed an appointment.
I had very weird experiences again this morning. An event I changed the day on a few weeks ago now went back to the original day it was scheduled for. I am pretty sure I did that on my phone, FWIW. But I can't specifically remember. Generally the point is to put it in the calendar so you can forget about it until the time you need to know. Well not anymore! I'd do better carrying a paper calendar/day planner the way this thing has been working.
An event I scheduled just this morning, for later in the day, done on my macbook, with travel time of 15 minutes, plus alerts 15 min and 5 minutes before travel time would NOT show up on my phone. Then it did for a few minutes, then it went away again while I was sitting here looking for answers and talking to my husband about it in iMessage.
So, I disabled iCloud from the ical prefs, which caused the event to disappear off the calendar entirely, then reenabled it, which caused it to reappear on both devices. But the phone version said I had an alert of 30 minutes and 20 minutes before travel time, and the macbook version was correct. ?!?! I changed the alerts on the phone to the correct ones, and it went to the macbook almost immediately but it did not replace the alerts, it just added them to what was currently there. So my macbook had four different alert times, and the iPhone had two. Then all of a sudden the macbook had three different 15 minute alerts, and one 5 minute alert. I deleted the extra ones off the macbook, and then my phone's version of the event alerts went to 30 minutes and 5 minutes. What the heck is going on?
I did discover that my iCloud settings (signed in with browser) were for the wrong time zone but that doesn't make any sense as to why the alerts were so messed up. And it wasn't like they were changing my appointment times or causing them to disappear entirely off the calendar. I fixed that but still would like to know what is going on.
And the sync problems are still messed up. It says I edited the event at 11:39 am which was when I was driving and I certainly wasn't editing calendar events. It told me this morning I had edited events at times when I was not editing anything and it wasn't just two hours off because of time zone issues either.
Now an event I edited this morning has an extra alert time in it on one device, but is correct in the other one.
