I don’t know how long you’ve had the Dual HDMI Tablo. But a few years ago, I had it for one day. Then I returned it, entirely because streaming video via my very robust network, was extremely unstable. I had the same experience you did with the buffering.
When I purchased it, I did it because it didn’t transcode the video, which rendered a better image quality, What I didn’t realize is that the Dual HDMI Tablo was really created for those who wanted a singular, plug-and-play direct connection from a DVR to their TV (via HDMI). And my hindsight impression is that is where Tablo put their focus for the Dual HDMI box.
Of course, that’s my perspective from my own experience. Others here may very well have some solutions for you.
If you do, beware that the 4th gen’s apps are not exactly free of bugs! But we have it in our home, on all newer model Rokus. And we really like it, save for the kinks, which they have to be working out.
One thing that’s worth repeating, since Tablo appears not to be communicating this well: Owners of 4th Gen Tablos, before doing any scans through a Roku Tablo app, should first perform the channel scan and select channels via the smartphone app.
There’s a bug in the Tablo Roku app’s channel setup that can cause the channels to jumble out of order in Roku… It can be fixed afterward, but it’s much less of a pain just to set it up on the phone app.