Symptoms
The vSAN ROBO license shows 0 virtual machines used.This can be checked under vCenter Server > Licenses > Global vSAN (VMware vSAN Standard for Retail and Branch Office) at column Usage > 0 VMs.
Cause
For vSAN, the VM consumption in not tracked, only CPUs are tracked. The VM usage is controlled by EULA agreement.
Resolution
This is a known issue affecting all vSAN versions with ROBO feature.