The TV is a 2 year old Panasonic OLED and has been working with the V6 flawlessly for the past 2 years.
I have taken note of previous posts on the board and have carried out the advise you suggested before posting.
The V6 is set to always on, directly connected to the TV with HDMI 2.0, software is up to date, factory reset an't happening because the TV is calibrated, but I can't see how this will make your box work.
The apps on the V6 shortly before the fail does not send a HDR signal to the TV, the same apps installed in the TV and from a Nvidia shield do.
I had to carry out a restart before I could change the resolution settings on the V6 because pressing continue sent the box into a black screen like Netflix.
Please can I remind you that everything works fine after the restart for a day or so and then apps HDR and DD stop working.
I find it hard to believe that it's a content protection issue on my part.
If there was a problem with the TV then this would also be showing from the in-built apps on the TV and the Nvidia.