Youtubetv frequently buffers

I can confirm that TMHI and YoutubeTV can work fine together with no inherent buffering problems.  Assuming you have good, consistent download speeds, your issue may be a weak WiFi connection with your TV.  Your TV may have tests for that, so that's one thing to check. Also, if your SSID for the 2.4 GHz and 5 Ghz channels are the same (which is the default config), you don't usually have control over which channel your TV "latches" on to.  The 5 GHz channel has much less range, and if your TV is latching to that and is not physically close enough to your router, it could definitely cause issues.  In that is the case, you need to force your TV to latch to the 2.4 GHz channel (which has much better range), If your TV doesn't allow that level of control, then you can make a unique SSID for the 2 channels on the TMHI Internet App and connect your TV to the 2.4 Ghz channel.

Same here. I have an excellent signal (all bars) on the gateway, and no issues with other Wi-Fi connected devices. So far, I haven't found a resolution. 

I think it's the YOUTUBETV App but YTTV blames internet.

What platforms/apps and what gateway are you using? YTTV works without buffering for me on iOS app, iPadOS app, MacOS Ventura app, Roku app, and via Chrome browser, on the Nokia gateway (the famous "trash can").

If you've only been using one platform/app, try it with a couple of different browsers and a different device. If none of them work properly, then it's likely something to do with your home internet or gateway settings.  If it works with some but not others, then you've probably eliminated the internet as the problem. Could be the apps or the settings on your device.

In addition, if your YTTV app is set up to use a high resolution stream (e.g., 4K), you can try using a lower resolution to help trouble shoot the prolemb. For example, my Roku device lets me specify a streaming resolution, and if I set it to a lower resolution, it uses less data per second.  This can be a diagnostic tool or temporary fix to reduce buffering.That said, I routinely view 4k programs on YTTV without buffering, so it should be possible to stream high res programming.

It's also possible that it might be related to the wifi setup on your gateway.  If the device having problems is using the 2.4G wifi band, it could be congestion on the 2.4G wifi band.  You might try switching to the 5G wifi to see if there's a difference.  Lots of info on this forum talking about how to do this, and the steps involved are dependent upon which gateway you have.

Good luck. This can be really frustrating until you can identify the exact cause. Before I retired, I was heavily involved with telecomm and networking. It can often be more black art than science, and the front-line support reps from either YTTV or TMHI aren't usually network specialists, but more often just following trouble shooting scripts to help identify the most likely problems and solutions.

GW to TV WIFI signal was key for. I bought a cheap WIFI extender and that has really helped with buffering.