After upgrading vCenter appliance to 7.0 Update 3 (7.0.3) there is an error displayed when accessing the Update tab (Lifecycle Manager) and logged in using a AD account.

According to the VMWare Knowledgebase article below there is currently no fix available but logging into vCenter using a @vsphere.local account allows access:

"Authentication failed, Lifecycle Manager server could not be contacted", Access to Lifecycle Manager fails in vCenter 7.0 Update 3 when logged in with an Active Directory account (85962) - https://kb.vmware.com/s/article/85962