in the content_fields.html.twig template, for the ezimage_field block, we have this piece of code

{% for attrname, attrvalue in attrs if attrvalue %}{{ attrname }}="{{ attrvalue }} " {% endfor %}

So, when you output an image using this default template you may end with something like <img src="img.jpg" width="400 " height="300 " />

Please note the blank spaces after the 400 and the 300.

This blank space make the w3c validator output erros saying things like

 Bad value 300   for attribute height on element img: Expected a digit but saw   instead.

From line 329, column 70; to line 329, column 202

Is an easy pick, i will take care of .