Xamrin UWP Release causes weird NullReferenceException (System.Security.Cryptography.PasswordDeriveBytes) - debugging

Question

public static class CryptoHelper {
// This size of the IV (in bytes) must = (keysize / 8). Default keysize is 256, so the IV must be
// 32 bytes long. Using a 16 character string here gives us 32 bytes when converted to a byte array.
private const string initVector = "pemgail9uzpgzl88";
// This constant is used to determine the keysize of the encryption algorithm
private static int keysize = 256;
private static int getKeySize()
{
return 256;
}
//Encrypt
//public static byte[] EncryptString( string plainText, string passPhrase ) {
public static byte[] EncryptString(string toEncrypt, string salt)
{
byte[] initVectorBytes = Encoding.UTF8.GetBytes(initVector);
byte[] plainTextBytes = Encoding.UTF8.GetBytes(toEncrypt);
byte[] keyBytes = new byte[126];
try
{
PasswordDeriveBytes password = new PasswordDeriveBytes(Encoding.UTF8.GetBytes(salt), null);
Debug.WriteLine(CryptoHelper.getKeySize());
Debug.WriteLine(password.ToString());
keyBytes = password.GetBytes(256 / 8);
} catch (Exception e)
{
Debug.WriteLine(e.StackTrace);
}
RijndaelManaged symmetricKey = new RijndaelManaged();
symmetricKey.Mode = CipherMode.CBC;
ICryptoTransform encryptor = symmetricKey.CreateEncryptor(keyBytes, initVectorBytes);
MemoryStream memoryStream = new MemoryStream();
CryptoStream cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write);
cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);
cryptoStream.FlushFinalBlock();
byte[] cipherTextBytes = memoryStream.ToArray();
memoryStream.Close();
cryptoStream.Close();
return cipherTextBytes;
}
........
The call to "password.GetBytes(256 / 8);" results in a non catchable NullReferenceException
This happens only when the UWP App is in Release mode; UWP Debug as well as Andorid and IOS are fine.
Also I get a weird Debug Message:
"this._hash" war "null".
or
"this._hash" was "null". (translated)
Here you can see it in action
VS2019 Screenshot
To repuduce this issue the inputs for the function are:
toEncrypt "Bearer eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzUxMiJ9.eyJzdWIiOiIxIiwiZXhwIjoxNjE3MDAyMTEyfQ.C0CaGgfibM4z55MoANI2CiohUyew09r3_D_TpcQ6n1c8LmQd8BusSyF1SMEIQ3cO5uxE9Tnau0ZAT6D3kN3NcQ"
salt
"9x83m74tzrx9387x4mz98374zt90x8m273z948734z59"
Cause I cant see the detailed cause of this problem there it is basilcy not possible to get a workaround for this.

Answer 1

I was trying to make the same code work. The solution I found was to replace:
PasswordDeriveBytes password = new PasswordDeriveBytes(Encoding.UTF8.GetBytes(salt), null);
with:
Rfc2898DeriveBytes password = new Rfc2898DeriveBytes(passPhrase, Encoding.UTF8.GetBytes("12345678"));
and also add this:
symmetricKey.Padding = PaddingMode.Zeros;