I have experienced this myself recently. I have had the same cable box and hdmi cable for a few years and did not start seeing this occur until I bought a new TV a few months ago. The only workaround I have seen myself outside of rebooting the box like you say is to change the display format to a 480 format and then change it back to 1080p in the contour settings menu. I have a Samsung QLED model Q80B. I had a different Samsung prior to this (non-QLED) and it worked without any issue. I think this may be a hdmi handshake issue as bluestar mentioned.
Brian
Cox Support Forum Moderator