I'm having the same exact issue. All sports channels and only sports channels (NESN, NBCSN, ComcastSN, ESPN, NFLN, etc....) are at times unwatchable. It's happening on all TV's with the lines coming from different splitters. The main TV is only split once. If the sporting event is on a regular broadcast network, no issues. The signal strength is good, I've done a system refresh, no change. There are times when it's OK, but when it's bad, it's really bad.
Comcast must be doing something to the sports channels that is an issue in my house and some other customers as well.
Unfortunately, trying to schedule a tech visit will be a challenge since it's very difficult to have someone home during normal business hours. I wish someone could give a hint that would explain the signal difference between sports channels and all other channels.
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