When you were setting up The Tablo Connect do you have a green check next to all 3 ports that can be opened? When I was setting mine up I wasn't certain if Tablo used all 3 ports, or if needed only one. its possible that it hops over to different ports for different interactions. Anyways I setup portforwarding on all 3 to be safe.
If you can ping externally I would say it is probably a device sync issue with the Tablo. Mainly that Tablo has "forgotten your devices" Not sure though.