Follow with a restart of the Winmgmt service:
Try querying with a different syntax:
# Run OMI command as LOCAL SYSTEM (highest privilege) psexec -s cmd cd "C:\Program Files\omi" omi query 'select * from Win32_OperatingSystem'
Get-CimInstance -ClassName Win32_OperatingSystem
: The querying user must be a member of the local Administrators group on the target machine.