Weird login behaviour using Azure AD B2C with Xamarin iOS - xamarin.forms

Question

We have a Xamarin Forms app that uses Azure AD B2C for login. I have followed this example code https://github.com/Azure-Samples/active-directory-b2c-xamarin-native
The Android version works perfectly. The workflow is seamless and works as expected.
On the iOS version we are getting some weird behaviour though.
Here is the flow on the iOS version of the app.
User launches the app and is presented with the Azure AD B2C login screen (correct)
User enters their credentials (correct)
The app redirects the user back to the login screen (with the username and password fields blank) (wrong)
After a few seconds the app then logs them in and navigates them to the main screen
After entering their credentials the user should be immediately navigated to the app main screen, NOT back to the login screen.
Once they are logged in, subsequently launching the app correctly logs them in. The problem is only on first login.
I can't seem to find any help on this anywhere. Is it the Safari browser, the token cache, something else? The code and workflow are correct as the Android version works perfectly, so it's something specific to the iOS app.
UPDATE
After some investigation it seems that this method may be causing the issue.
public override bool OpenUrl(UIApplication app, NSUrl url, NSDictionary options)
{
AuthenticationContinuationHelper.SetAuthenticationContinuationEventArgs(url);
return true;
}
According to the docs
this logic is meant to ensure that once the interactive portion of the
authentication flow is concluded, the flow goes back to MSAL
But it doesn't. It redirects the user back to the OnAppearing() method of the login page where it attempts (again) to acquire a token (which it does).
Is there any way to fix the behaviour of this method?
AuthenticationContinuationHelper.SetAuthenticationContinuationEventArgs(url)
UPDATE2
Here is the login code (simplified for clarity)
protected override async void OnAppearing()
{
base.OnAppearing();
// Check to see if we have a User in the cache already.
try
{
IEnumerable<IAccount> accounts = await AuthenticationService.PCA().GetAccountsAsync();
var account = this.GetAccountByPolicy(accounts, ApplicationConstants.SignUpSignInPolicy);
AuthenticationResult ar = await AuthenticationService.PCA().AcquireTokenSilentAsync(ApplicationConstants.Scopes, account, ApplicationConstants.Authority, false);
}
catch (Exception)
{
// Doesn't matter, we go in interactive mode
this.OnSignIn();
}
}
private async void OnSignIn()
{
try
{
IEnumerable<IAccount> accounts = await AuthenticationService.PCA().GetAccountsAsync();
var account = this.GetAccountByPolicy(accounts, ApplicationConstants.SignUpSignInPolicy);
AuthenticationResult ar = await AuthenticationService.PCA().AcquireTokenAsync(ApplicationConstants.Scopes, account, App.UiParent);
}
catch (Exception ex)
{
InstanceManager.LoggingHelper().TrackError(ex);
// Checking the exception message
// should ONLY be done for B2C
// reset and not any other error.
if (ex.Message.Contains("AADB2C90118"))
{
this.OnPasswordReset();
}
else
{
await DisplayAlert(StringConstants.ExceptionText, StringConstants.AuthenticationError, StringConstants.CloseDialog);
this.OnSignIn();
}
}
}