Hi @bloke!
It is happening with just one category? Other products are sorted correctly?
If this is the case, it is strange behavior.
Could you please try performing a conflict test and check if it helps to solve the issue?
You can do this by temporarily switching your theme back to Storefront, disabling all plugins except WooCommerce, and then check again if the issue persists.
If that solves it, reactivate the theme first and check again. Then, reactivate your other plugins, testing after each, until you find the one causing conflict.
If you cannot perform a conflict test on your live site, we recommend creating a staging site using the WP Staging plugin.
You can find a more detailed explanation of how to do a conflict test here: https://docs.woocommerce.com/document/how-to-test-for-conflicts/.
Let us know how that goes for you!