Getting 400 Bad Request response when uploading large file directly to amazon s3 bucket

I've followed this tutorial: http://ift.tt/1jrbSst

Everything works fine except when I try to upload large files. I also enabled file chunking and set the max file size for a chunk to 5mb. Yet the error still persists, randomly appears whenever I try to upload a file that's about 70mb. Sometimes it even works but most of the time it doesn't.

Here's the response I'm getting:

Remote Address:54.231.17.48:80
Request URL:http://ift.tt/1LEBhWc
Request Method:POST
Status Code:400 Bad Request

response headers:

Access-Control-Allow-Methods:HEAD, GET, PUT, POST, DELETE
Access-Control-Allow-Origin:*
Access-Control-Expose-Headers:ETag, x-amz-meta-custom-header
Access-Control-Max-Age:30000
Connection:close
Content-Type:application/xml
Date:Mon, 12 Oct 2015 14:07:00 GMT
Server:AmazonS3
Transfer-Encoding:chunked
Vary:Origin, Access-Control-Request-Headers, Access-Control-Request-Method
x-amz-id-...
x-amz-request-id:...

How can I make this work? It works some of the time but not all of the time.