Bad logo resizing with a message of onload="pagespeed.CriticalImages…

Hi, I have a urgent problem. I prepared a website on a test domain (altervista). Then I migrated the site to the final domain. To do that I exported first everything as xml file. Then I installed WP on the final domain, I installed the various plugins and then re-imported the xml. Finally I imported the theme settings. I must say it is the first time I use this method to migrate a web site, as normally I was copying the whole wp folder, importing the database (after having changed the urls)

However everything worked well, except for the logo. My web site has the home page wth a full screen slider, on which I added a transparent logo. In the following pages there is a standard header with coloured logo. The logo in the following pages however looks shrinked and the inspection of the code by firebug gives me this message

<strong class="logo">
<a href="http://www.marinemammalhabitat.org/">
<script data-pagespeed-no-defer="">
<img src="http://www.marinemammalhabitat.org/wp-content/themes/mmpatf/images/300x100xmmpatf-small.png.pagespeed.ic.0U97kyRcd-.png" alt="Marine Mammal Protected Areas Task Force" data-pagespeed-url-hash="1616380742" onload="pagespeed.CriticalImages.checkImageForCriticality(this);" height="100" width="300">
</a>
</strong

Consider that the image file I use has the following name: “mmpatf-small.png”

This did not happened with the testing web site. I tried to upload a different logo but it gives me the same problem. I also tried to upload it from the media files libraru but with no success

Any idea? Thanks