Ports 80, and 8887 are the internal (private) ports used for Tablo Remote Connect.
Ports 21050, and 21051 are the external (public/internet) ports that are used for Tablo Remote Connect to connect from the internet to your Tablo.
For each of the 2 port forwarding rules…
Source Ports should be set to ANY. (This one throws off a lot of people.)
Destination Ports should be set to the external (public/internet) port for each rule: 21050 for one, and 21051 for the other.
Forward to Port should be set to 80 for the 21050 destination.
Forward to Port should be set to 8887 for the 21051 destination.