Question Build error on UWP form ARM 32 with an external dll and an async function

Hello

We have an issue when building for UWP - ARM32 (Hololens2)
We have a dll with async functions like this:

Code (CSharp):

1. using System;
2. using System.Collections.Generic;
3. using System.Linq;
4. using System.Net.Http;
5. using System.Runtime.InteropServices;
6. using System.Text;
7. using System.Text.RegularExpressions;
8. using System.Threading.Tasks;
9.  
10. namespace TestClassLib
11. {
12.     public class TestClass1
13.     {
14.         private readonly HttpClient _httpClient = new HttpClient();
15.  
16.      
17.         public async Task<int> GetDotNetCountAsync()
18.         {
19.             // Suspends GetDotNetCount() to allow the caller (the web server)
20.             // to accept another request, rather than blocking on this one.
21.             var html = await _httpClient.GetStringAsync("https://dotnetfoundation.org");
22.  
23.             return Regex.Matches(html, @"\.NET").Count;
24.         }
25.  
26.         public int GetDotNetCount()
27.         {
28.          
29.  
30.             return GetDotNetCountAsync().Result;
31.         }
32.  
33.  
34.     }
35. }
36.  

It's compiled for ARM 32/Release. In an unity script if we call the synchrone function everythings works, but if we await on the async function over the dll boundary the build breaks.

Code (csharp):

1.  
2. #if UNITY_WSA && !UNITY_EDITOR
3. TestClass1 t = new TestClass1();
4. int n = t.GetDotNetCount(); //this works
5.  
6. int n2 = await t.GetDotNetCountAsync(); //this breaks the build
7. #endif
8.  

Build error is error CS1705: Assembly 'ClassLib' with identity 'ClassLib, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' uses 'System.Runtime, Version=4.2.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' which has a higher version than referenced assembly 'System.Runtime' with identity 'System.Runtime, Version=4.1.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'

Any clue would be welcome. Thanks for reading