The likely problem is with Shaw (Bell has this problem too). To make a VERY complex answer to it's most least common denominators, it could be 1: Over compression to the bird. 2: Buffer under-run at the bird. Buffer Under-run is when more data than the buffers on the sat can handle during the transponder inversion process so that the NAK packet to the ground station to halt xmission until the buffer being used has room to take more data, so that the NAK packet received and processed after the ground buffer's resend cache has been flushed so that the desired resend of the data packet is no longer available to be resent to the bird.
Buffer under-run happens more often during Prime Time, in each time zone. i.e. 1900hrs~2300hrs EST is 1600hrs~2000hrs in the West but affects BOTH times zones simultaneously. West Prime Time is from 1900hrs~2300hrs PST. Prime Time programming is usually more high resolution, high def programming which means MORE datum trying to transit the transponders. Buffer under-run exhibits as data noise, or also known as data artifacts. Usually display on your TV as lots of little squares and/or screen lock. As long as these entertainment providers, like Shaw, Bell and the Big Networks, continue to try to force more datum through the Transponders than the buffers can handle, this situation will continue.