I got some help from Tablo support. Posting here for the rest of the internet.
The key problem is that my router, as others above have noted, doesn’t support forwarding external ports to different internal ports. The solution was two steps: (1) Putting the Tablo in the DMZ; (2) changing the port mapping in Tablo setup map to the same port numbers.
- Log in to your router
- Click ‘Advanced Setup’
3 Click ‘DMZ Hosting’ - Click ‘enable’
- Enter the Tablo’s IP address: 192.168.10.7
- Apply or save
Note: Some routers need to be rebooted after making these changes. - Delete the port forwarding rules you made earlier
- Go to the Tablo web app http://my.tablotv.com or Tablo app on a smartphone or tablet
9 Go to ‘settings’ - In the Tablo Connect section, change the ports so they look like this
80 -> 80
8887 -> 8887 - Click ‘retest port mapping’