FB.ui share_open_graph strange dialog behaviour

I need to implement URL sharing on Facebook via javascript, sharing also a picture. When the FB sharing dialog appears, it starts shrinking itself and keeps shrinking more and more until it becomes about 20 pixels wide.

And it happens using either the share_open_graph or "share" method.

Also, on the JS console i see this error when the sharing dialog appears:

ErrorUtils caught an error: "<![EX[["Could not find element \"%s\"%s 
from module \"%s\"","u_0_18","","__el...". 
Subsequent errors won't be logged; see https://fburl.com/debugjs.

This is my code:

<script>
    $(document).ready(function() {
        $.ajaxSetup({ cache: true });
        $.getScript('//connect.facebook.net/en_US/sdk.js', function(){
            FB.init({
                appId: '476337039102253',
                version: 'v2.8'
            });
            FB.getLoginStatus(APP.fbUpdateStatusCallback);

        });            
});
</script>

<button id="itb" class="btn btn-primary btn-large active_down" name="btn" onclick="
            FB.ui({
                method: 'share_open_graph',
                action_type: 'og.shares',
                action_properties: JSON.stringify({
                    object: {
                        'og:url': 'https://example.com',
                        'og:title': 'page title',
                        'og:description': 'desc',
                        'og:image': 'https://savebybooking.s3.amazonaws.com/public/prd/File_341'
                    }
                })             
            }, function(response){
                if (response &amp;&amp; !response.error_message) {
                  console.log('fb sharing OK: '+JSON.stringify(response));
                } else {
                 console.log('Not OK: '+JSON.stringify(response));
                }
           }); return false;" type="submit">Share</button>

Are you having the same issue? Why is it happening? I used the "share" method until yesterday without problems, this issue appeared today with no modification to my code.

p.s. I prefer using share_open_graph rather than share method because the latter won't let you share the specified picture but seems to pick a random image from the url you are sharing.