Yep this is a known issue in wplms as of now .
to quick fix that please follow these steps :
Goto wp-admin -> plugins -> editor .
Select vibe custom types plugin to edit .
Select meta_box.php to edit .
Find admin_enqueue_scripts function in metabox .php file .
Replace this line :
if(in_array($post_type,array('course','quiz','unit','news','wplms-assignment','wplms-event','question','post','testimonial','popup','certificate'))){
with this :
if(in_array($post_type,array('course','quiz','unit','news','wplms-assignment','wplms-event','question','page','post','testimonial','popup','certificate'))){
then save the changes .
refer : http://prntscr.com/a9af65