I have a model year 2018 Q8FN82. I bought it in Feburary/March of 2019.
Note, in the external device manager, the HDMI UHD Color setting is on for HDMI 1 (my only input used). I run a Sheild TV Pro through an onkyo TX-RZ810 which then runs to the HDMI 1 port on the TV, both set to output HDR.
I'm not sure how long this issues been going on, but it's at least 3 months. I started noted that my picture didn't look quite right and when I checked my TV's settings HDR was no longer active. I know for a fact it was previously active through the TV picture menu.
I went through every device confirming they were set for 4K HDR. I made sure the content I was playing was HDR. I restarted reset the Sheild and receiver and nothing would get the TV to reflect HDR. Eventually, I did a full reset on the TV and set it up again, now getting it to reflect HDR.
Unfortunately, some time later (not sure how long) the TV no longer reflected HDR again on HDR sources. let's just say I went through multiple resets to factory, always fixing the issue, but the issue always returning. Eventually I decided to start messing with the HDMI UHD Color settings, wondering if it had an impact. My first test was just switching to HDMI 2 with UHD color settings on while the TV was no longer showing HDR. What I found was that the TV, after recognizing the new input, was reflecting HDR.
So, that got me curious about the HDMI 1 input itself. I returned to using that input and the next time the TV 'lost' HDR, I simply unplugged the cable, plugged it back in, and HDR was back. Now, I wanted to rule out the cable, so I swapped through at least 3 high quality cables all finding the same exact result - eventually the TV loses HDR, but unplugging the cable and plugging the cable back in solves it. I even did swaps on the HDMI cable from the Shield to the receiver, but the result was always the same.
I wondered if the TV was doing this cycle every time I power cycled it (turned it on and off), but, right after fixing the issue through unplugging the HDMI cable from the TV and plugging it back in, I turned everything off, turned everything back on, and HDR was still there. That means, it's dropping at some point, but with an unknown cause. I just 'fixed' the issue again on Monday. It is now Thursday, and it still shows HDR. In some unknown time, probably next week, it will no longer reflect HDR and I'll have to unplug the HDMI cable and plug it back in.
Has anyone else experienced this type of issue? Any known fixes? It seems to be the TV as the source of the problem.