Hello @razvantamasanu,
Thank you for contacting Rank Math support, and sorry for any inconvenience that might have been caused due to that.
This is the order we follow to generate meta descriptions for WooCommerce products or product categories for that matter:
1. Content from SEO Description field
If that is missing, then:
2. WooCommerce Excerpt or Product Short Description
If that is missing, then:
3. Template From General Settings in WordPress Dashboard > Rank Math > Titles & Meta > Products
If that is missing, then:
4. Auto-generated Content from the product page.
However, if you wanted to force the use of the description you have set in Global product settings (Rank math > Titles & meta > Products > Single Product Description), you can customize the following filter to target your products only and apply it to your site:
https://rankmath.com/kb/filters-hooks-api-developer/#use-global-meta-description
Hope that helps.