Okay, fingers truly fucking crossed here, but it appears as if my replacement TV no longer has the blackout issue. As I said, fingers crossed, but right now, and it has been about an hour, I have not seen the issue and have had 4k enabled on both my Roku 4 and One S (of course).
Two things to note...
1) The HDMI 5 port on this TV is way more "snug" than my previous model. The cable fits real tight. On my previous TV, from the very beginning, it obviously fit and went in, but it never fit like this.
2) The firmware version on this new replacement is different from my previous TV. Was my previous TV never updating its firmware even though it claimed to be? I do not know, but here is the info from original set to the newer set.
Original
Version 1.3.15-UHD
FRC Version 9.406
New TV
Version 1.3.26-UHD
FRC Version 9.415
Was that all it was? And if so, why was my previous TV not installing the firmware updates? I also have to admit, I have no idea what FRC is or means, Googling it looks like it may be Frame Rate Converter?? If so I would definitely imagine having a newer version of it could be a factor as well.
Whatever it may be, I am really happy. No HDR for me, but I finally get to experience 4K with no issues. Again, fingers crossed it stays this way.