I am developing mobile app based on Phonegap / Cordova. Sometimes there is lack of internet connection. This plugin works fine on that situation, but sometimes there is problem with localStorage (throws QuotaExceededError if length exceeds about 5 MB - it is browser specific thing). Probably that storage in Webwiev is not efficent as expected. Maybe it would be better using WebSQL with Persistence.js - we can set its capacity up to 50MB.
Yes, you are correct that localstorage is full. You can either work on efficiency or use an IndexedDB (or deprecated WebSQL) backend instead. See #149 (comment) and #73 on how to use other backends with this library.