Usually, the local storage data persists until removed from the app.
We can try to reproduce your case but for that purpose we will need some more details like targeting framework and device model and version you are testing on.
I would suggest testing on another device just to be sure it is not device specific issue. You can also debug your app on the device
and check whether you have any populated data in Developer tools > Resources tab.
You can store data in a SQLite database using the SQLite plugin
but for a small data I guess it is better to use the Local Storage.