Hi, I'm sorry to hear that you're experiencing an issue with Thunderbird's calendar. From what you've described, it seems that some of your due events are being removed or hidden in Thunderbird, even though they are present in your CalDAV server and mobile devices. To troubleshoot this issue, I would recommend trying the following steps: Check Thunderbird's calendar settings: Go to Thunderbird's Options or Preferences menu and navigate to the Calendar section. Make sure that all calendars are enabled and properly synced with your CalDAV server. Verify event dismissal settings: Thunderbird allows you to dismiss events, which may hide them from view. Check if you have any settings enabled that automatically dismiss events after a certain period of time. Adjust these settings if necessary. Review Thunderbird's filter options: Thunderbird provides filtering options that allow you to customize the display of events. Make sure that you haven't accidentally applied any filters that could be hiding certain events. If none of these steps resolve the issue, I would recommend posting your question on the Thunderbird Support Forum. There, other Thunderbird users and volunteers can provide further assistance and help troubleshoot the problem. Please let me know if there's anything else I can do to assist you.