Xamarin ADAL AcquireTokenAsync not returning from await

I got this code:

        public async Task<MultipleAuthResult> Authenticate(string authority, string resource, string resource2, string clientId, string returnUri)
        {
          MultipleAuthResult multipleAuth = new MultipleAuthResult();
          var authContext = new AuthenticationContext(authority);
          if (authContext.TokenCache.ReadItems().Any())
              authContext = new AuthenticationContext(authContext.TokenCache.ReadItems().First().Authority);

          var uri = new Uri(returnUri);
          var platformParams = new PlatformParameters((Activity)Xamarin.Forms.Forms.Context);
          try
          {
              multipleAuth.ResultBackEnd = await authContext.AcquireTokenAsync(resource, clientId, uri, platformParams); 

          }
          catch (AdalException e)
          {
              return null;
          }

          return multipleAuth;
        }

When I try to get the token, in my Xamarin.Form droid, The Azure login page pop up I can log into it. After the Azure page close, but the line

multipleAuth.ResultBackEnd = await authContext.AcquireTokenAsync(resource, clientId, uri, platformParams); 

never come back for the await. No exception, no visible error.

When I retry, Azure do not ask for my login information. The login page open and close rapidly. (Cached token I think). But my code do not go out from the await. What I do wrong? I use:

• Xamarin.Form 4.4
• Microsoft.IdentityModel.Clients.ActiveDirectory 5.2.7