I've been working with an app that uses Google to login for the past 10 years, and I've had problems with sub changing when these situations happened : - Domain change - Company being bought by another one and being integrated in their Google Workspace - Employee leaving and coming back

To us, it's very very far from the quoted 0.04% which is to me very high. I had to deal with it 5-6 times in the past 10 years but of course that number will vary depending on the usage of your app and I'm not gonna venture and put a percentage on it.