Please make the full backup of your site and check the issue on the Storefront theme to detect if our theme causes the problem. Storefront is a free theme developed by WooСommerce.
If you see the problem on WoodMart only, please check and reactive the template for a single product in the Dashboard > Layouts.
If the vendor does not appear on the product page, it means the functionality does not assume that.
Alternatively, you can show brand attributes on the product page, if you do not use the brand, you can create a vendor name and logo instead: https://xtemos.com/docs-topic/product-brands/
If you have any questions please feel free to contact us.