I started using the app together on my MacBook and iPhone. Faced the following problems:
If you snooze a reminder via notification on your MacBook, the Alert Time doesn't change automatically when you change the Due Time for this reminder via iPhone. The old value remains. This happens until you delete Alert Time and manually set It to the same value as Due Time (it doesn't matter on which device).
If you do something with a reminder via a notification on your MacBook (snooze or complete), the notification will remain in the notification center on your iPhone. If, on the contrary, you do something with the reminder via a notification on your iPhone (snooze or complete), then the notification will disappear on your MacBook after a short time (4-5 seconds).
P.S. Is it normal that are no notifications about calendar events on any device?