I have a 4 day old qn85a. When playing 4k content using my firestick I can not access any menus to change pic settings. Pressing home key does nothing. Occasionally it may pop up after 4 seconds. exiting movie still no good. I've had it lock up that power down and up gets it working until streaming 4k again. I think the processor is over taxed. I'm an old TV technician. Software up to date. 1904. Not happy and likely returning it. I contacted chat last night with an unusual remote problem. I finally resolved the issue. But. they were supposed to contact me today. They did not. I'm calling tomorrow on this issue.
I found out using the app does not cause the problem. I'm going to try another port. Also, another bug report. Watching in movie mode then exiting to Amazon Prime menu is blazing bright. They need a menu brightness toggle like a low high.
Update: When using the firestick. Go into display settings and set match original frame rate to off. That fixes the menu issue while streaming 4k content. Side note. Using the stick for Netflix, Disney and Amazon Prime look better to me vs using the built in tv apps.