tepidt

Dragos,

I just ran into this same problem, did a google search, your result came up. Did some more searching and this is the solution that I found that worked for me.

WordPress 4.4 made some changes to how images are loaded.
https://make.wordpress.org/core/2015/11/10/responsive-images-in-wordpress-4-4/

It allows the browser to pick the default size, and especially on mobile it will use the Medium image size and not the Large size. Hence, you’re seeing the reduced quality. Your theme may need to be updated to account for this new change, if not already.

As for me I have an old theme that is no longer supported so I’m doing a work around.

The work around that I found is to change the medium image size to match my actual full size. Under Setting -> Media, you should see Medium and Large. I changed the values to match as I currently do not have any responsive design, you can change it to whatever you prefer.

Of course that change by itself will not work because your medium images have already been generated so you will need to regenerate those images. Here is the site that helped: ‘Regenerate Thumbnails’

Once my images were regenerated, everything loaded clearly as expected on mobile. My mobile display matches my desktop display.

I hope this points you in the right direction and hopefully provide a solution?

Thanks,

T