Xamarin Forms UWP Azure B2C IdentityProvider Login failed - azure

Question

I have already implemented this: https://github.com/Azure-Samples/active-directory-b2c-xamarin-native sample into an external app, but i got errors while login with an openid identity provider.
To reproduce this problem I checked out the latest master of the sample, tried to reproduce this error within the solution and it also occurs there.
I just changed the B2CConstants file values and everything is working for local accounts.
In my Azure B2C I have created 2 identity providers for different AD's in my signin/signup policy.
For Android and iOS everything works fine as expected, also the login with the identity provider.
If I log in with the UWP App via the identity provider i get the following error:
"We can't connect to the service you need right now. Check your network connection or try this again later."
This message shows up in the external Popup Window after Login (normally it should redirect back to the App without error)
In my external app, sometimes its possible to login via the identity provider if I first login with local account ⇒ logout and login again with identity provider credentials. But its not really a workaround because the error comes again on the next login.
I configured the identity provider with following documentation:
https://learn.microsoft.com/de-de/azure/active-directory-b2c/tutorial-add-identity-providers
I tried following things:
add Capabilities:
<Capabilities>
<Capability Name="internetClient" />
<uap:Capability Name="enterpriseAuthentication"/>
<Capability Name="privateNetworkClientServer"/>
<uap:Capability Name="sharedUserCertificates"/>
<uap:Capability Name="userAccountInformation"/>
<Capability Name="internetClientServer"/>
</Capabilities>
found it here:
https://github.com/Azure-Samples/active-directory-b2c-xamarin-native/issues/137
And tried also setting the registry and redirect url which is created from the app during execution:
https://github.com/AzureAD/microsoft-authentication-library-for-dotnet/wiki/UWP-specifics#properties-of-platformparameter-specific-to-winrt-and-uwp-corporate-network
some additional information, I developed the identity provider login with a signIn/signUp (default) policy, that was working at the beginning, the error occurs only sometimes.
After I changed to a only signin (default) policy, the error occurs nearly every time (only works with the workaround which i described already).
Im not quite sure what im missing or doing wrong, hope someone can help me.
Thank you!