Dropzone.js uploads only two files when autoProcessQueue set to false
Add parallelUploads: 10(This is your max no)
There's a simple way to solve this which can be found here:
https://github.com/enyo/dropzone/issues/253#issuecomment-22184190
"If you want autoProcessQueue to be true after the first upload, then just listen to the processing event, and set this.options.autoProcessQueue = true; inside."
So just add
this.on("processing", function() {
this.options.autoProcessQueue = true;
});