Azure AD B2C Single Sign Out - azure-ad-b2c

Question

I have two web apps, one a .Net Framework app and the other a .Net Core app. Both are registered with the same B2C environment.
They interact with one another such that when I sign in on one application, when I click on sign in on the other, this takes me past the input screen and logs me in with the credentials already entered on the other application.
The issue I have is that I have set up a Logout Url for both applications, but it is only working one way round and not the other.
If I am logged in on both applications, then sign out of the Framework application, then when pressing F5 on the Core application, the user is logged out as expected.
However, if I try this the other way round. So I sign out of the Core application, then press F5 on the Framework application, then this does not log the user out.
As it is working one way but not the other, I assume this must be an issue with how the Framework application is setup and not with how the Custom Policy files linked to each application are setup, as if it was, then neither would work?
In the B2C application setting for the Framework application, the Logout URL is:
https://xxxx.azurewebsites.net/Account/SignOut
Which points to:
public void SignOut()
{
if (Request.IsAuthenticated)
{
IEnumerable<AuthenticationDescription> authTypes = HttpContext.GetOwinContext().Authentication.GetAuthenticationTypes();
HttpContext.GetOwinContext().Authentication.SignOut(authTypes.Select(t => t.AuthenticationType).ToArray());
Request.GetOwinContext().Authentication.GetAuthenticationTypes();
}
}
I've also tried an endpoint which is the same as the above but doesn't check if the user is currently authenticated, and just runs the three lines without the if check, but that doesn't work either.
While, the B2C application settings for the Core application, the Logout URL is:
https://yyyy.azurewebsites.net/AzureADB2C/Account/SignOut
Any ideas?