WP_Scripts::localize was called incorrectly code example
Example: WP_Scripts::localize was called incorrectly.
# Befor
wp_localize_script( 'wlsm-admin', 'wlsmloadingtext', 'Loading...');
# After
wp_localize_script( 'wlsm-admin', 'wlsmloadingtext', ['Loading...'] );
you can fix that by passing in an array