Calender doesn't upade properly when it's opened

Reinstall this software.

Ensure you have a stable internet connection, as many calendars sync data online. If there's a refresh button or option, use it to manually update the calendar.

If you're using a cloud-based calendar service like Google Calendar or Microsoft Exchange, check for any sync issues:

1.Sign in to your calendar account online.
2.Check if there are any sync errors or issues with your calendar data.
3.If you find any issues, try resolving them by following the provider's instructions.

dud it's default calender app. It's just a bug. I know what's going on, I've posted this to get attention of the developer.

Refresh Calendar: find the refresh button or drop down refresh function in the app to manually update events.
Check Internet Connection: make sure your device is connected to the Internet to synchronize calendar updates.
Sync Settings:
Google Calendar: go to Settings, select Account, turn on Sync to try to clear cache or data
Outlook: check account settings and make sure synchronization is turned on.
Update app: Check and install the latest update for the Calendar app in the App Store.
Reboot device: Turn off the device and then turn it back on to resolve temporary issues.
Delete and re-add accounts: Delete accounts from the Calendar app and re-add them to restore synchronization.
Check for conflicting events: Ensure that there are no conflicting events that are preventing the calendar from updating.
Check calendar settings: Confirm all relevant calendars are enabled and displayed in the app settings