I was going to install patches in my vSphere 6.7 environment today using Update Manager, and ran into an issue in the HTML5 client  as I clicked on the Updates tab for a host.   I received a red warning box with the following error message:

Response with Status: 401 OK for URL

I tried logging out and back into the VCSA as well as an appliance restart but the problem remained.  After some more digging, I found this is a known issue on the Firefox browser and how it caches pages in vSphere 6.7.    VMware is looking into it.   For the moment, the workaround is to disable caching in Firefox (or use a different browser).

To disable caching in Firefox

1. In the Firefox address bar type:  about:config
2. Search for browser.cache.disk.enable
3. Double-click true and it will toggle to false.
4. restart Firefox

You can read more details on this issue by visiting the VMware Knowledge Base:  KB59696