I purchased a newer Belkin (AC1200) router to replace an older Belkin. The new one was fast and worked great but I could never get it to cooperate with Tablo. I even worked with Tablo support. The older one was just too old and started to struggle with everything. I finally replaced them with a Netgear R6400 and it’s been smooth sailing since.
If you are trying to manually setup port forwarding make sure UPnP is turned off. If it has UPnP.