When you say you save the custom “description” tab are you talking about a tab that you created and named description? Or are you talking about the default WooCommerce description tab isn’t showing up?
Tabs are a feature of WooCommerce which is filtered to allow more tabs to be applied to their template. Themes can also add these template files as well so that they can change the styling.
If you can go onto the WooCommerce product edit page and edit, save and view your tabs in the WordPress admin your’re not having a tabs issue you’re having a template issue.
I would start off by getting to know the template structure first and how you can override that in a child theme. From there you may be able to implement templates in your theme.
Template Structure:
https://docs.woocommerce.com/document/template-structure/
Have a great rest of your day!
– Freddie