It certainly sounds to me that this need to be escalated up the Infiniti/Nissan food-chain. In my neck of the woods (Philadelphia) we have ABC consumer affairs advocate Nydia Han who will promote an issue like this on her show and then brow-beat the manufacturers for a resolution she can then report on, possibly including the dealer. Merely threatening someone within Nissan that you might press forward along an avenue like this might get results.
I am especially interested in whether or not this is an isolated issue or if others are experiencing the same thing. My wife just bought a new left-over 2019 QX50 ‘Essential’ with the Pro-Pilot assist safety suite and so far (three weeks in), so good. As a retired manufacturing professional I can attest to the possibility, however slight in 2018/2019, that something went awry in the manufacturing process affecting this one and only vehicle. Where electronics are concerned almost anything is possible; an intermittent short, or loss of ground (which should be redundantly designed), could cause intermittent problems and be nearly impossible to diagnose in the shop, even if they witness the problem. This type of problem could be the source of a collage of problems that defines the car as a true ‘lemon’. If so, time for Nydia Han.
Then again, the QX50 for 2019 is a completely different vehicle than the one it replaced. I was so impressed with my wife’s vehicle that I went out and found a fully loaded 2017 QX50 for myself; one that has the same set of safety features. Almost everything mechanical/physical is different between the two of them however, most likely including the very complex collection of wiring-harnesses. While the software governing all these systems’ operations might be the same the mechanical signal interconnections most likely are not. This car, and perhaps many more like it, may simply be suffering from ‘first-year-blues’ that Infiniti/Nissan will correct in later years after they sort out the root of the problem. My 2017 was the last year of production for the J50, which hopefully means that all the previous years’ gremlins had been exorcised for the 2016/17 models. I have the perfect base of comparison to see behavior differences between the two vehicles.
In the meantime, you might as well start some wheels rolling to get your car replaced. If the dealer has done nothing to correct the problem, then there is no reason to expect that it might magically have corrected itself. And electronics problems are oftentimes the most difficult to sort out......especially if they’re rooted in some mechanical wiring problem. Then again, maybe they did change something in the software, something for which an oncoming revision will correct it. But who knows when/if Infiniti will do that? Get the wheels rolling, you don’t want to have to live with this!!