wordpress get_the_post_thumbnail can’t set size

I have wordpress with multisite, so it will be pc and mobile version.
On my pc version, i can use wp_get_attachment_image_src(get_post_thumbnail_id($id), array('210','210'))

But on my mobile version, it doesn’t work.
I can get the image but the size didn’t change.

Do anyone know why? Do i need to set something else?
Thank you