Hi Hector
I use my theme thumbnail for the widget rather than the built-in thumbail functionality (via the wpp_parse_custom_content_tags filter). I just use a simple get_the_post_thumbnail($post_id, 'my-size') to generate the html output. This outputs all the normal attributes that it outputs elsewhere (e.g. title and srcset etc) however the sizes attribute doesn’t appear. Even if I try to force one by using get_the_post_thumbnail($post_id, 'my-size', array('sizes' => '40px')) it doesn’t appear in the eventual output. I can add any other attribute that I want (e.g. get_the_post_thumbnail($post_id, 'my-sizes', array('data-sizes' => '40px')) works as expected and I get a data-sizes attribute output to the page.
So it looks like something is somehow sanitizing or otherwise removing the sizes attribute. This attribute does work on all the other image displays on my site so it isn’t a site-wide problem, it only doesn’t work within WPP as far as I can tell. Do you have any ideas what could be causing this, or any suggestions for how I might fix it? I did try using the wpp_post filter instead but the problem still remains with that too.
Cheers