C# Mongodb FindOneAndReplace or ReplaceOne is not working

Question

public async Task SomeWork()
        {
            Debug.WriteLine("SomeWork for User : " + Context.User.Identity.Name);
            var userProfile = await UserProfileCollection.Find(u => u._id == Context.User.Identity.Name).FirstOrDefaultAsync();

            userProfile.SuccessfullConnect = true; // currently false
            var up = await UserProfileCollection.FindOneAndReplaceAsync(u => u._id == userProfile._id, userProfile);
            Debug.WriteLine(ObjectDumper.Dump(userProfile));
            Debug.WriteLine(ObjectDumper.Dump(up));
            Debug.WriteLine("Saved SomeWork for User : " + Context.User.Identity.Name);
        }

Below is the debug output. My document is not getting replaced. Check SuccessfullConnect variable it is still false. I checked on server also document is not replaced. And sometime its working and sometime its not working.

SomeWork for User : +919933221101
{TestSignalR_Server.Models.UserProfile}
  _id: "+919933221101"
  ...
  SuccessfullConnect: True
  ...

{TestSignalR_Server.Models.UserProfile}
  _id: "+919933221101"
  ...
  SuccessfullConnect: False
  ...

Saved SomeWork for User : +919933221101

Answer 1

Method FindOneAndReplaceAsync should work fine.
But by default this method returns origin document. You can change ReturnDocument to ReturnDocument.After to see document after changes.

var options = new FindOneAndReplaceOptions<Profile>
{
     ReturnDocument = ReturnDocument.After
};
var up = await collection.FindOneAndReplaceAsync<Profile>(u => u._id == userProfile._id, userProfile, options);