Here is another idea. And this is what I intend to do. Perhaps I cut and replace one cable end at a time and install a new connector. I have found these connectors which appear to be the correct specs (50 ohm):
https://www.digikey.com/product-detail/en/molex-llc/0733660010/WM5539-ND/1465161 (right angle)
https://www.digikey.com/product-detail/en/molex-llc/0733660020/WM5388-ND/2755904 (straight)
I mean, for under $10 including shipping I can try new ends. This is not rocket science. I doubt the cable is crimped somewhere. If its faulty, it is probably end related. Maybe the pin is not long enough on an existing end and there is a momentary intermittant gap.
I am going to try this and purchase some RG174 cable as well (the spec for the Blackvue Cable can be found here:
https://www.blackvue.com/product/coaxial-cable/
I will order a few ends for testing purposes and make my own test cable and if it works, I will cut and install new ends on the main cable. Worst case scenerio is that I &^%$ up the main cable and then I will get it replaced anyway as part of the final thing I can do to get this working.
Edit: This is all ordered. I will get to the bottom of this if it is the last. thing. I. ever. do.
Edit 2: I am now hyper-focused on the theory that the center pin on one or the other (or both) ends of the coaxial cable is too short. The basis of this theory is a post I came across somewhere that said the rear camera cannot be "hot swapped" and power must be removed and reapplied to connect the rear camera again. If this is true, it would follow that a momentary "open" connection, no matter how brief, would cause a rear camera disconnect which would not recover even if the connection was restored. This explains why removing power and re-applying power always fixes the issue. Ruling out both cameras now as a cause, and making an assumption this is not a design or software issue, and making a further assumption that the wire itself is not faulty (coax is pretty tough), and making a final assumption that the ground sleeve on the MCX plug clearly has a snug fit, all signs point toward a center pin that, while visibly straight, is too short literally by under a millimeter. Think of your two opposite fingertips barely touching. Break the bond momentarily and the camera dies until power is removed and restored. This is easy enough to fix by replacing the ends of the cable without needing to go back to the shop (I am skilled enough to do this myself). I will make a test cable before I cut the operational cable. I ordered this -
https://www.amazon.com/gp/B016EBRQAA - which matches the cable description on the Blackvue spec page. If the test cable works, I will leave that in place draped to the rear of the car for a few days and see what happens. If it still drops, i will give up. But at least I have a plan. I think I may be right as to the problem. As for OCD that the cable end at the main camera may be silver or look odd, I can get this cover and hide it:
https://www.blackvue.com/tamper-proof-case/
I will update as I go. It may take until mid next week to get the connectors in the mail.