I have an older Yamaha with an LG TV that exhibits a similar problem.
The SHAW box cannot go through the Yamaha because the sound for YouTube, etc. must come from the TV,
so I use optical from the TV to the Yamaha.
Occasionally the center channel would drop out, typically on recordings, during switches from commercials to program.
All that could be heard was surround sound until I backed up and replayed the section where the switch occurred.
This usually brought back center channel.
Although my problem is with the sound, where exactly is it originating: SHAW box signal, TV optical output, or Yamaha input?
Try changing cable box sound output method on your system, Dolby/Stereo/PCM, to see what works.