since a couple updates ago, iOS is not fully compatible with Google Cloud service. Some users (a minority) are unable to log in.
Best solution would be to use an own version for cloud save. Give the player the option to choose where the file should be stored. There is no need to develop it yourself, you can use FOSS solutions like that https://github.com/cryptomator/cryptomator
Use the given libraries for sync to gdrive Dropbox and Co, or at least a simple ftp. That way you'll be independent of Google, Apple or steam or their updates.
Just my 2 cent, of course you're busy with the next game, but maybe you could use that idea for Archaelund first, to avoid such problems in the future