We understand that some users are having issue with your account being logged out after updated to 3.1/3.1.1, and then you are unable to log in again with Facebook.
For some other users, even after successful log in, the app will auto log-out your account after a while.
We are investigating the cause of this issue right now. We'll keep you updated once we have identified a permanent fix for it. For now, please take a look at the workarounds below:
WARNING: The workarounds below may cause you to lose the data that haven’t been backed up in Manga Rock.
Work-around #1: A user reported that you will be able to log-in again after a quick deleting/reinstalling the app.
Work-around #2: You can go to your Device Settings > Storage & USB > Apps Storage > Manga Rock > Choose "Clear Data". After that you should be able to login normally again.
Affected version: Android 3.1 and above
First reported case: Oct 5, 2017
Resolved date: TBA