Hello together,
I know i am late to the party and there is already a solution, but I had a similar problem with a different cause.
Setting:
VCSA 7.0.3 (Build 22357613 - Patch U3o) on a Fujitsu Primergy 2530 M5 installed with ESXi 7.0.3 (Build 22348816 - Patch U3o)
So I tried to activate EVC on a cluster with six hosts - all hosts are 2530 M5's. I had a Problem with only one specific host which kept EVC activation to end in an error. It was said that there are powered-on VMs with different EVC CPU Mode, but all VMs on that specific hosts seemed finde with the genereation I wanted to use.
My solution was, that there was one single VM, that hadnt had an entry for the EVC CPU Mode - some old Linux VM. Since the VM had no entry, the Cluster EVC activation somehow always failed. So i just shut down the VM and i worked fine. After booting the VM back up in the EVC activated cluster, it directly had the EVC Mode Entry, that was missing.
So keep an eye out for powered-on VMs, that doesnt have an entry for EVC Mode. Perhaps they cause the same issue for your enviorment.