I seem to have found the cause of my issue. Since I've made the change I have not encountered the problem again.
I actually worked with a few different Comcast service reps (they were very knowledgeable/helpful!) - started by troubleshooting with settings on the box and settings on the TV. Ultimately in an earlier post/thread I remember seeing the HDMI link option (that had been on Comcast Labs) worked for one person but that was removed from options.
Searching options on my TV I found the CEC was turned on. There are probably more technical people on this thread that can explain better but since that was on it was causing my issue. More on CEC: http://encyclopedia2.thefreedictionary.com/hdmi+cec
Once I turned the CEC option off on my TV, I have not had the problem since!
I'm not sure for Samsung/Sony if the option would use the same term as Vizio, but I would suggest searching your TV settings for this to turn it off - reading that CEC still has some kinks across vendor products.
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Spoke with a rep last night after going through all the solutions suggested here.. I get a no signal on my Vizio p65 4K. I thought it was due to it going to sleep after a certain amount of time, however the rep told me to adjust the system update time to see if that was causing the issue... and sure enough after changing to 6pm instead of running at 4am, I turned the tv on next day with no issue. However turned it back on at 9pm and there was the no signal.. do others see the same thing?
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