I’m following up on this closed topic, since I had the same problem last week.
I updated WooCommerce locally from 3.8 to 4.0 and I can recall clicking the Woocommerce database upgrade after that. Everything still seemed to be working correctly so I pushed my changes to staging & production.
I’m pretty sure I never saw the Woocommerce database upgrade button on staging or production, while I have seen it before on other major updates. This caused losing a lot of connected attributes terms on my products and therefore broken product variations.
Any idea what might have caused this?
My client would like to know how to prevent this in the future