I know this sounds like a super generic problem, but I'm finding that live TV streams are buffering significantly more with the Roku than with other devices. Actually, they don't buffer at all with other devices. This is a Roku Express, so maybe that's the issue?
I can watch the exact same channel at the same time with zero buffering on my iPhone while the Roku stream buffers every 5-10 seconds, which I would imagine eliminates issues regarding network quality or buffering due to a slow server (it's a 32 thread dual Xeon). According to my UniFi access point, the Roku has 98% signal quality (as it should, considering the AP is about 5 feet away).
Any ideas? Let me know if you need any logs or other info.