Dropzone.js progressbar not updating on emit using s3.managedUpload - dropzone.js

Question

I found a couple of examples on how to do AWS uploads with dropzone.js testing them independently and now I'm trying to combine them into a finished form for our website's image uploader.
The one example I found showed that you could trigger progress updates from the S3.managedUpload as follows:
file.s3upload.on('httpUploadProgress', function(progress) {
if (progress.total) {
var percent = ((progress.loaded * 100) / progress.total);
console.log('httpUploadProgress', percent, progress.loaded);
myDropzone.emit('uploadprogress', file, percent, progress.loaded);
}
});
With my console.log in there, I can see multiple loops of the httpUploadProgress with increasing percentage. But the {dropzone}.emit doesn't seem to update the progress bar.
I've tried using the external 'myDropzone' var as well as making my AWSSendFile function (where the above code is included) as a prototype of dropzone itself so I can refer to it with this.emit(). No luck.
The dropzone template is:
dropzoneTemplate:'
<div class="Item dropzone-previews">
<div class="Icon"><img data-dz-thumbnail /></div>
<div class="Description dz-preview dz-file-preview">
<span class="Filename" data-dz-name ></span><br/>
<div class="dz-progress"><span class="dz-upload dz-progress" data-dz-uploadprogress ></span></div>
</div>
</div>'
Full code with the prototyped functions:
// override the uploadFiles function to send via AWS SDK instead of xhr
Dropzone.prototype.uploadFiles = function (files) {
for (var j = 0; j < files.length; j++) {
var file = files[j];
this.AWSsendFile(file);
}
};
Dropzone.prototype.AWSsendFile = function(file) {
let dz = this;
file.s3upload.send(function(err, data) {
if (err) {
dz.emit("error", file, err.message);
} else {
dz.emit("complete", file);
}
});
// listen to the AWS httpUploadProgress event, and emit an equivalent Dropzone event
file.s3upload.on('httpUploadProgress', function(progress) {
if (progress.total) {
var percent = ((progress.loaded * 100) / progress.total);
console.log('httpUploadProgress', percent, progress.loaded);
dz.emit('uploadprogress', file, percent, progress.loaded);
}
});
};
function acceptCallback(file, done) {
// options for the managed upload for this accepted file
// define the bucket, and the S3 key the file will be stored as
let fullKey = userId + "/" + file.name;
let params = {
Bucket: bucket,
Key: fullKey,
Body: file,
Region: 'us-east-2'
};
// add an S3 managed upload instance to the file
file.s3upload = new AWS.S3.ManagedUpload({params: params});
done();
};
function abortUpload(file) {
if (file.s3upload) file.s3upload.abort();
};
example console.log data:
httpUploadProgress 97.33840304182509 49152
httpUploadProgress 100 50496
UPDATE:
I noticed one problem with the async embedded callbacks and modified the 'prototyped' functions above to show my changes. Setting a local variable for dz = this to hold the handle of the main dropzone object. This makes the progress bar work hunky-dory and it now goes to 100%, but now the 'complete' emit call doesn't seem to be telling it to show as complete.