In the process of upgrading the first of 3 ESXi hosts from 6.0U2 to 6.5U1 (from VCSA 6.5) I found my first host stuck at the following screen.
How do I proceed?
Were you using a custom vendor ESXi server image for your platform? Look like a driver issue.
Check the drivers your hosts are running and make sure they're in the compatibility matrix.
That’s caused by network adapter firmware, you have to upgrade server network adapter firmware. I would recommend you upgrade firmware of each component version.