From 2.3.6 to 3.1.5

[pedrollanesbenchmark]

I have upgraded to version 3.1.5 and I can see that it's not working now. when I see in the back code this lines

var formValues = UploaderFormValues(context.Request.Form);

// check the upload control vars are correct
var files = context.Request.Files;
if (files.Count == 0 || !formValues.ContainsKey("queuedCount") || !formValues.ContainsKey("uploadedCount") || !formValues.ContainsKey("uploaderID"))
{
    return;
}

I can see that the values of this keys are not existing. Why?