Spotlight not working with Netgear ReadyNAS
Try looking into this Netgear KB article https://kb.netgear.com/000045492/ReadyNAS-OS-6-8-File-Search


  Enabling File Search
  
  To enable File Search on your ReadyNAS, 
  
  
  Click System > Settings.
  Under Services, click File Search.
  Check the Enabled box, then click Apply.
  
  
  File Search can also be enabled from the System > Overview screen.





  File Search via Finder on macOS
  
  If you use macOS, File Search integrates with Spotlight on SMB and AFP connections to ReadyNAS shares. If your share is set to be indexed and is mounted on your macOS, Spotlight will not have to use additional resources to scan the share. NETGEAR recommends using SMB instead of AFP and enabling .