Hi,
I have the same problem, when doing an add, it opens extra slow and sometimes returns a 504 error. This is the query statement I see from the database when opening the database.
SELECT SQL_CALC_FOUND_ROWS wp_posts.ID FROM wp_posts INNER JOIN wp_postmeta ON ( wp_posts.ID = wp_postmeta.post_id ) INNER JOIN wp_postmeta AS mt1 ON ( wp_posts.ID = mt1.post_id ) WHERE 1=1 AND (
( wp_postmeta.meta_key = 'prod-chart' AND wp_postmeta.meta_value = '484298' )
OR
( mt1.meta_key = 'prod-chart' AND mt1.meta_value LIKE '%[484298,%' )
OR
( mt1.meta_key = 'prod-chart' AND mt1.meta_value LIKE '%,484298,%' )
OR
( mt1.meta_key = 'prod-chart' AND mt1.meta_value LIKE '%,484298]%' )
OR
( mt1.meta_key = 'prod-chart' AND mt1.meta_value LIKE '%[484298]%' )
) AND wp_posts.post_type = 'product' AND (wp_posts.post_status = 'publish' OR wp_posts.post_status = 'future' OR wp_posts.post_status = 'draft' OR wp_posts.post_status = 'pending' OR wp_posts.post_status = 'private') GROUP BY wp_posts.ID ORDER BY wp_postmeta.meta_value DESC LIMIT 0, 10
I upgraded the plugin version to: 2.2.3 for this problem.