Empty warning message related to compatibility is visible on the Upgrade Plan wizard.
"Unable to verify the compatibility for the following product versions. Please check the product documentation before proceeding to upgrade:"
In VCF 5.1 the false warning is shown when attempting to PLAN UPGRADE.
1. In the SDDC Manager UI go to "Workload Domains" then select the required domain.
2. Select "Updates" then click "PLAN UPGRADE" button
3. There is false warning shown with the message "Unable to verify the compatibility for the following product versions. Please check the product documentation before proceeding to upgrade:"
If there are no product names and versions mentioned in the message (as shown in the screenshot above), the message can safely be ignored. Please continue with the upgrade planning wizard and click the "CONFIRM" button.