I was updating one of my customer’s environment to vCenter 8.0 Update 3a today and was from the old vSphere Update Manager Baselines over to image based updating via vSphere Lifecycle Manager (vLCM), but the compliance check stopped at 30% for some reason.
I had a look through lifecycle.log and found several timeout errors.
It turns out that vCenter 8.0 Update 3a changes how vSphere Lifecycle Manager downloads updates for ESXi hosts and if port 9087 is not open between the ESXi hosts and vCenter it fails. This is documented in the release notes for vCenter 8.0 Update 3, but is very easily missed.
Therefore, if you have issues with the compliance check make sure that port 9087 is open between the ESXi hosts and vCenter.