After installing and configuring Omnivore for Magento 2, you end up with all your products in a "DEFAULT CATEGORY"
See below
This bug was addressed in the latest Magento 2 version 2.3.4, so please upgrade to this version to resolve the issue.
It can be found here https://magento.com/tech-resources/download
Additional information:
https://github.com/magento/magento2/issues/25269
https://github.com/magento/magento2/issues/25837
https://devdocs.magento.com/guides/v2.3/release-notes/release-notes-2-3-4-open-source.html