Form submitted twice, due to :remote=>true

On Rails 5, rails-ujs replaces jquery_ujs. Events will trigger twice if both are required.

// app/assets/javascripts/application.js
//= require jquery_ujs <-- delete this
//= require rails-ujs

It seems that Ryan Muller's answer is correct. But removing application.js is not proper way to do as per my view. What I have done is I have opened the developer's tool in chrome and click on network part. Now when I click on submit button then it would show me that who is making request. So I removed that JS and tried it again and it works. So as per Ryan Muller its correct that its problem of JS by including twice. But make sure you maintain the dependency of JS as well.

I am assuming that you are using jquery. This is usually happened when there is an incomplete call or there is some sort of error and you haven't refresh the page. Try something like this:

<script type="text/javascript">
$('#new_product_group_form').submit(function() {
                    $(this).unbind('submit').submit();
       });
</script>

In case people are stumbling on this question like I did:

I had the same problem, and sannankhalid's answer didn't fix it, but deleting a locally precompiled application.js in the public/assets directory did -- the ujs is included twice, so it fires twice. Via https://stackoverflow.com/a/9627690/604093