FT virtual machines in a cluster that is activated with vSphere DRS do not function correctly if Enhanced vMotion Compatibility (EVC) is currently deactivated.
Because EVC is a prerequisite for using DRS with FT VMs, DRS does not place or evacuate them if EVC has been deactivated (even if it is later reactivated).
When EVC is deactivated on a DRS cluster, a VM override that deactivates DRS on an FT VM might be added. Even if EVC is later reactivated, this override is not canceled.
If DRS does not place or evacuate FT VMs in the cluster, check the VMs for a VM override that is deactivating DRS. If you find one, remove the override that is deactivating DRS.