Symptoms:
Virtual machines (VM) with Skylake EVC mode enabled experience:

• Powering on VMs show no value for the EVC Mode in the vSphere Client > VMs tab.
• The ESXi host build is prior to 6.7P02
• VMs previously powered on while on a ESXi 6.7P02 or earlier host.
• After one of these actions
  • Adding a standalone Skylake generation host to an existing Skylake EVC mode cluster
  • Migrating a virtual machine on a standalone Skylake generation host to a host in an Skylake EVC mode cluster
  • Enabling Skylake EVC mode on a cluster of Skylake generation hosts that have virtual machines powered on

VMware vSphere ESXi 6.7
VMware vCenter Server 7.0.x
VMware vCenter Server 6.7.x
VMware vSphere ESXi 7.0.0

This issue occurs due to:

• Skylake EVC mode not expose the Memory Protection Extensions (MPX) feature. This MPX feature is supported and exposed only on standalone ESXi hosts.
• VMs with virtual hardware version less than 13 are not exposed to any Skylake CPU features so will not show Skylake as their 'EVC Mode'. If the EVC Mode is empty, no masking of features will occur.

This is expected behavior.

Starting with ESXi 6.7 P02 and ESXi 7.0 GA, in order to minimize disruptions during future upgrades, VMware will no longer expose MPX by default to VMs at power-on. A VM configuration option can be used to continue exposing MPX. For more information, see MPX Feature Deprecation in Virtual Machines

Memory protection extensions (MPX) were introduced in Skylake and provided hardware support for bound checking. However, Intel began removing the MPX feature beginning with Ice Lake CPUs. As such, while this feature continues to be supported, it will not be exposed by default to virtual machines at power-on and is not included at the EVC baseline level.

Workaround:
To work around this issue, enable EVC at the virtual machine level to maintain mobility to hosts in the datacenter or in the cloud. For more information, see Enhanced vMotion Compatibility as a Virtual Machine Attribute section of the VMware vSphere Product Documentation.

If this is not possible due to some unmet requirements, VMware recommends to enable EVC at the cluster level and avoid migrating from standalone ESXi hosts.

Note: The minimum supported hardware version for MPX is hardware version 13, this issue is only occurs on VMs over HW version 12.

MPX Feature Deprecation in Virtual Machines
VMware EVC and CPU Compatibility FAQ
vCenter Server 7.0 services fails to start in an EVC enabled cluster
“The target host does not support the virtual machine’s current hardware requirements” error vMotioning a VM