FireTV + Plex black screen during playback

Server Version#: 1.40.2.8351 (Synology DSM 6)
Player Version#: 10.13.0.466 (cf77d59a)
FireTV 4K Max (2nd Gen) OS Version: 8.1.0.3 (RS8103/2083)

FireTV → AVR → TV.

The Plex server is running primarily on my DS1815+ (DSM 6.2)

While watching a video in Plex on the FireTV 4K Max, the screen will suddenly go black while the audio continues to play. That suggests that Plex is still operating as per normal.

So far, the issue happens randomly with no discernible pattern. I have not seen this occur while watching content in another app, but I primarily use Plex on this FireTV.

I am not 100% sure what is causing this issue, although I do suspect it is the FireTV, but I cannot rule out any obscure interaction between Plex and the FireTV. It may also be my TV or AVR at fault, but I have not been able to determine which just yet.

After the black screen appears, if I turn off the FireTV and then turn it back on, sometimes the black screen remains and sometimes not.

I have disconnected power from the FireTV when the black screen remains before reconnecting power and this restores the video output, so that seems to suggest an issue with the FireTV, but I still cannot be certain of that, it may be the TV is not responding to the FireTV correctly or it may even be my AVR/HDMI connections?

I checked for an update for the FireTV OS and one was available. However, after installing the update, the version of OS did not change?

I checked my other identical FireTV 4K Max for an update, but it did not offer any and the OS version is identical to the problem FireTV and I have not seen the issue on this FireTV at all.

Has anyone else experienced this issue?

Does anyone have any hints/tips on diagnosing this issue?

The issue with the sudden black screen turned out to be an issue with the HDMI cable between my AVR and TV.

It was not the Fire TV or Plex as I first suspected.

The cable has been replaced and so far, so good.