Old or future events not showing up in aCalendar? This is usually a sync limitation of your cloud service – not an aCalendar bug. Here is what you can do about it.
Why events go missing
aCalendar does not store any calendar data itself. It only displays what Android has synced from your cloud service. If events are missing, it means they were never synced to your phone – aCalendar cannot show what isn’t there.
Many cloud services only sync a limited time window to your phone – for example the last 12 months and the next 12 months. Events outside that window exist online but are simply not downloaded to your device.
Google Calendar
Google only syncs events from roughly the past 12 months and the next 12 months to Android. Events outside that window are only available at calendar.google.com in a web browser.
Note: The Google Calendar app uses its own sync system that includes older data – but this data is locked in and not shared with other calendar apps like aCalendar.
Extend the sync time window aCalendar+ / Business
In the Calendar List (Menu → Manage Calendars), tap the three-dot menu next to a Google calendar. You can set the future sync window to 1, 3 or 5 years, and request a re-sync of the past 3 calendar years.
Note: the future sync window is set per account, not per individual calendar. You may still need to use the manual workaround below for very old events.
Manual workaround for Google
This trick forces Google to re-sync old events by updating their “last modified” timestamp. It needs to be repeated every 12 months if you need continued access to older events.
After re-importing, wait a few minutes and then trigger a manual sync in aCalendar (Menu → Manage Calendars → three dots → Sync now). The missing events should then appear.