Social Connection Logout (Google and Facebook) federated takes user to strange places

I am trying to implement social login using a webview from within a Unity application. I have connected Google and Facebook as social connections.

Login works well, but logout is confusing me because the user ends up at strange places.

It might be relevant that I am using a webview within a cross platform app. So on desktop it will ‘pop out’ as a web view browser, while on iOS it will use a more native browser to iOS.
The browser package we are using is uniwebview

What I’m experiencing is I will open a web view to logout (I think I need to do that, because federated logout may direct the user to other places depending on the login used?),
Then if they were logged in with google, they end up here
Or if they were logged in with facebook they end up here

Neither case will let the user end up where I expect them to (the &returnTo= param given, which is a return to the uniwebview which I can use to receive an event that the logout is complete).
I should also mention that if a user is logged in directly with us (a database connection through Auth0), and we ask them to logout, still with the ?federated query param - it all works and the user ends up at returnTo where we close the browser and continue after logout.

Here is an example of the logout url I am opening with the webview:

And here are screenshots showing where the user ends up:
If logged in with Google, user ends up at

If logged in with Facebook, user ends up at

Please help me understand how to troubleshoot further or logout the same way for any logins.
We are also planning on adding “Sign in with Apple” so it would be good to know if this has any gotchas regarding logout too.
Thanks so much!