I've been pulling my hair out trying to figure out why my popular products were not displaying total sales count descending. It seemed to be somewhat random.
I found this code in template_functions.php => mp_popular_products:
The custom query has this parameter to order the display of popular products: &orderby=meta_value, where mp_sales_count => meta_value.
After researching the wp codex I found this: https://codex.wordpress.org/Class_Reference/WP_Query#Type_Parameters
I changed order by to &orderby=meta_value_num
My popular products are now properly displaying most sales descending.
Is there another cause for this display order issue?
Thought I would pass it on for explanation and possible fix in a future release.