[Potential Fix] App found Base Station but was offline. Deleted and start over and now works.
I have the Costco Arlo Pro 2 VCS3000c. On initial set up the app identified the base station but said it was offline. I rebooted router with no change as being offline in app. I deleted the device (base station) to start over. Now I can reconnect to the base. All three lights are green.