This has been plaguing me for months and I can't figure out what's causing it.
I use calendar and alerts to remind me of many things I need to do throughout the day. Normally I have my default alert set as 1 hour, but I have some things that I don't need a 1-hour early alert on, I just want to be notified at the time of the event and maybe 5 minutes before.
So I go into my repeating event in Calendar on either my iMac or my Macbook, and change the default alert to "At time of event", and I have one other alert at say 5 or 10 minutes early. It asks me if I want to apply to future events which of course I say yes, and everything looks fine. I can quit & relaunch Calendar, everything reflects correctly.
Then suddenly the next day when the appointed time comes, I get an alert 1 hour ahead of time. Wondering wtf is going on, I open Calendar and look at the alert. Sure enough... it's back to my default alert being 1 hour early. I check yesterday's appointment and it, too, is set to 1 hour early. All occurrences are. It's as if I never made the change.
How can I get these alert changes I make, to stick?
EDIT: To make things stranger... on my iMac yesterday, I deleted the offending event and created it from scratch, with only the two desired alerts. It has appeared to behave fine, as today it is not alerting me an hour ahead of time like it was before.
But, on my MacBook... that very same new calendar event appears due to iCloud, but it does show the 1-hour early alert in addition to the two alerts I actually set, and is alerting me an hour early. My iPhone SE is also alerting me an hour early. I have logged completely out of iCloud on my MacBook and back in, and rebooted, and the MacBook calendar still shows the incorrect extra alert. I'm stumped. Seems like some kind of strange iCloud issue but I can't figure out what.
Now for an extra sanity check, on my iMac just now I logged out of iCloud and back in, and sure enough... my calendar event now has that pesky extra "default" alert at one hour early. What the heck is going on here?