Migrating problem – featured images

The_post_thumbnail is a function that “runs” on the “theme” side of things.. not the DB.

in short – you need to have a theme that supports post thumbnails .
That means , to have it work – you need the SAME theme when migrating to be functional , OR adapt the new one.

Open your functions.php on your theme, and search for something like :

add_theme_support( 'post-thumbnails' ); //thumnails
set_post_thumbnail_size( 230, 150, true ); // Normal post thumbnails

AND the following :

//add_image_size( 'single-post-thumbnail', 400, 9999 ); // Permalink thumbnail size choose one !
add_image_size( 'single-post-thumbnail', 400, 300,true ); // single-post-test
add_image_size( 'tooltip', 100, 100, true ); // Permalink thumbnail size
add_image_size( 'nivo', 470, 350, true ); // nivo slider size

note that the names and size in your theme will be different.

If you do not have it on your OLD, you will need to copy that from your OLD theme´s functions.php , to your NEW theme – along with the proper the_post_thumbnail_(arg) that appear on your theme files (like single.php, archives.php etc..)

The simplest way (if you are a beginner in WP) is to activate the old theme on the new migration site and see if all works..

Also – check that the folder structure, permalink structure AND folders/files naming are all the same..