I have noticed this as well starting yesterday on both My Roku TV and today on my Roku Premier.
This is ONLY on the Roku Channel and I am using Live TV on the Roku Channel.
My Connection is Excellent and I have even switched Wifi Networks and it is the same.
The Connection is Excellent and the speed is 39bps.
Google Wifi Speed test is 589MBps down 25 up.
I have rest the device and still have the same issue.
Also, It doesn't actually say it's buffering on the Premier screen, it just goes black for a few seconds then comes back on.