Symptoms:

Following an upgrade to vCenter 6.7 Update 1, Update Manager intermittently encounters a "401 OK" response status when accessing a specific URL within the Firefox browser. 

Sample error message from the vCenter UI during a host scan:

Response with status: 401 OK for URL: example.com/ui/vum-ui/rest/vcobjects/urn:vmomi:HostSystem:host-##:########-####-####-####-############/isUpdateSupported

VMware vCenter Server 6.7

This is an expected behavior from a session validation security feature against an expired session from browser cache.

This issue is resolved in VMware vCenter 6.7 Update 2.

Workaround:
To workaround this issue, use a different browser or clear/disable browser cache on Firefox and retry:

• Please refer to respective browser documentation to clear the cache:
  • How to clear the Firefox cache
  • How do I stop Firefox from caching pages?

Disclaimer: Broadcom is not responsible for the reliability of any data, opinions, advice, or statements made on third-party websites. Inclusion of such links does not imply that Broadcom endorses, recommends, or accepts any responsibility for the content of such sites.