This app is using iCloud sync'ing.
Sometimes there some problems may occur. For instance, you checked items on one device and these changes doesn't appear on second device.
In some difficult cases, the data changes protocol may lost. In this case the app will crash.
Best solution for fix all data in this app is... to delelte app from device, wait for a minute and re-install it from App Store. All data will be downloaded from iCloud.
If you composed some important list for you and want to save it, just send it yourself by e-mail. To do it, open your list and tap Export in right-upper corner. Then choose Export by e-mail.
The list will be sent as file. You can save it wherever you want. Further you can open this file in Baggage app and get your list.