I am amazed i have not myself had the rear camera connection issue, CUZ i have been testing quite a few 2 or more channel cameras since that became possible.
But ! if the rear camera connection are a bit flaky it can take down the whole system, so its not just a matter of the rear camera coming and going. It is fine for a clean boot with or without any remote cameras connected, but if one camera disconnect after boot, that trigger all kinds of problems for the system.
And its not like i am super gentle installing a new system in the car, at least not at first, but if its a feel good system i might update it to primary system and the most prime location on my windscreen, and so a new install are often needed.
As you have tried that many memory cards, i very much doubt that is the problem, i am more inclined to guess towards problematic rear camera wire or plug ( for instance a hatch back car like mine ) you do not want a lot of slack wire at the rear camera, that can cause the plug to wiggle loose.
Also the power source, some are tempted to use a USB charge plug in the car, but even today with fast charge phones these in car USB plugs are often very weak.
The same go for some multi port USB chargers people might get to be able to do more things with the one 12 V plug in their dash, and while these often claim to be 2 A on each socket, thats often not correct, and then a camera get starved for power, and will behave erratic on boot but also during general operation.
Hence why i said that if you use a " creative " power source, you should try the provided one that came with the camera.
TBH i have a little problem accepting the wire getting broken, unless you install the system with 2 hammers, in my eyes the wires i had dealt with have always felt sturdy.
Okay the little coaxial wires and plugs on some newer viofo cameras, do / did have me a little worried as they are only 50% diameter of the USB wires we most see used, but i have now tried a couple of cameras using that rear camera connection and for me it have worked just fine and i must say the thinner wires, and smaller plugs, are a dream to work with during install.
So much so that when i installed the A 139 camera i was sent i immediately routed the wire thru the cable rubber grommet to my rear hatch, CUZ with the easy to work with cable it was not really any extra work for me.
Now the rear camera unit can of course also be broken, but from keeping taps on things in here, that seem to be very rare VS the broken wire.
There are also the issue of incompatible memory cards, this is a real issue but in most brands its not super hard to buy a working card, on the flip side other big name brands seem to go out of their way to ensure as little as possible work with their model.
My suite of memory cards to test this with are at 12 cards ( 256 GB ones ) and most often most of those will work in any dashcam, but testing the viofo A 229 duo i did run into 3 brand new cards in a row that did not work there, but those 3 cards then worked just fine in the vantrue system i was also testing at the time. And of course in my dji action camera and other stuff i tried those cards in.
Also some of those " viofo problematic " cards, also appear to work just fine in a 70mai system i am testing ATM, so for sure viofo just had a hickup there, but plenty of other cards work just fine.
