[UPDATE 15.12.2019] Google has released a fix for the issue that is causing problems at sign-in. Please update 'Google Play Games' on your device.
There is currently a known issue with the new update version 25.1.2 on Android devices, where the game does not load when switching between accounts.
We are currently investigating and hope to fix the issue as soon as possible. Our apologies for any inconvenience caused by this issue!