If you did not enable Backup before changing your device, doing a factory reset, or deleting the app, your entries will be lost, and instead, you will see red question marks on your calendar.

Logging into your Leap Second Account on a new device, after reinstalling Leap Second or performing a factory reset, and then enabling Backup will not restore your entries.

Your Leap Second account will try to recover your entries but won't be able to. This results in the red question marks appearing on your Calendar view.

Those unsuccessful recoveries will not appear on your exports. To remove them from your Calendar view, you can select each one and delete them as you would with a regular entry.
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For more information about Backups, please check the following article collection: Backups.