There are a few aspects of WooCommerce's inventory that are not actively supported by Thrive.
Below are the most common restrictions:
Products marked as "downloadable"
Thrive does NOT track downloadable products. You can still track them in WooCommerce, but they will not appear in Thrive.
Selectable variations (a.k.a. "variants")
Products with selectable variations in WooCommerce must be assigned to a single attribute term in WooCommerce.
Products that are not simple or variable types in WooCommerce