since the Android 9 update calendar notifications are very unreliable on my Fairphone 2. In most cases, they appear with a large delay of several hours or when I manually open the calendar. This is a bit frustrating. Any help is appreciated.
I am using the stock calendar app with Offline Calendar to keep my calendars on the phone without any synchronization. I also tried Etar as an alternative to the stock calendar app and Simple Calendar Pro as a standalone offline calendar app. I deactivated battery optimization for these apps. I tried various settings for the notifications (sound, vibration on/off). But still calendar notifications are very unreliable. Other notifications (messengers, alarm clock) are working as expected.
I am on Fairphone Open 21.12.0-rel.1, but it also happened with earlier versions of Android 9.