It's possible you have accidentally deleted an important checklist.
No worries: you can easily restore checklists that were deleted in the past 14 days.
Simply click on the Restore button for any checklist you wish to restore
Your checklist will be restored. You can click on any other deleted checklist.
Click on the My Account link at the bottom of the Trash bin to go back to your account and see the restored checklist(s).
Restored checklists will have all their tasks marked as open. This is a normal part of restoration.