Hey did you ever get this fixed? It seems to be inconsistent, sometimes it works and other times not. At the moment I am using a dirty workaround that asks the player to first log in before being able to sync from the cloud. I'd much rather use the login async event to trigger a cloud_synchnorize() call.
No, once player logs in I save this in an .ini file. I check this file afterwards up until the player calls achievement_logout. I'll insert a social async callback to silent login function. (I don't know how to deal with it yet)
--
Some functions do not work properly that I had to play around the extension myself.
The plugin does not support many of the things that Google Play Services offer.
The plugin uses outdated api versions.
The plugin & Game Maker Studio 2's core uses outdated and to-be-removed services (Such as Google Cloud Messaging).
Since my Firebase extension finished, I think I can write a better version of this once I have some free time.