Update 2.5.3:

You can now log in again. Please make sure that you have downloaded version 2.5.3 from the stores beforehand. Users of the browser version automatically have the latest version.

Version 2.5.3 contains many improvements:

Revision of the Custommatch lobbies for more reliability
Numerous fixes for issues that could cause users to get stuck in a “Find running game” loop
Fixed issues with the UI that could cause a display error after a CATAN Gold purchase
Increased server stability and reliability in times of high demand
Fixed issues with the AI that could cause games to stop running