There are some reasons that lead to fail to backup/restore, i.e. using Manga Rock Cloud.
Problem with Manga Rock's server
In many cases, the main problem is Manga Rock’s server. When our server experiences downtime, we can’t save your data.
Please try again later. Normally, our server is only down for a short time. We're very sorry about this unwanted experiences.
Problem with backing up big data
In some extreme cases, you might have hundreds of manga in Favorites and Recent. Backing up or restoring these data might fail sometimes.
We highly recommend that you edit and remove certain manga from your Favorites or Recent lists. The ideal number is about 100 manga for Favorites, and 50 manga for Recent.
Problem with corrupted data
For some cases, this issue is due to corrupted data. It happens when you back up your data using poor Internet connection and your data can't be backed up properly.
If you have tried and failed at all the methods in the article, please consider reinstalling the app. We have many users report that reinstalling the app might help to fix this issue.
For Play Store users, since the app only has one English source, which is Manga Rock source (check out this article to know the reason), some manga series might lost, please contact our in-app Support System so that we can manually restore data for you. Or you can use the Manga Rock Definitive version for unlimited access to diverse manga series together with many other benefits and features.
Otherwise, please wait until the next release of Manga Rock (both iOS and Android). Our team is working hard to fix this bug permanently.