the_post_thumbnail does not use an updated add_image_size

Dear all,

I changed one of the sizes in the theme’s functions.php from ad_image_size( ‘content-img’, 300, 168, true ) to add_image_size( ‘content-img’, 660, 660, false );. However for whatever reason the_post_thumbnail( ‘content-img’ ); still uses the old settings.

I switched to another theme and back in a hope it has something to do with php cashing but this did not help. Waited couple of days but it is the same. I don’t use any caching plugins (unless JetPack does some caching which I am not aware of; Photon part of JetPack is deactivated)

Any ideas how to approach this issue?

Regards,
Denis.