Did you check the display URL in the Roon settings?
Sometime my display don’t work and I found that the port for the display has changed.
A question from my side: when I use display in Firefox on the FireTV I have the problem that after half an hour the FireTv shuts down, because of supposed inactivity. Did you found a workaroud for this?
Yeah mine was working last year, but not anymore. One thing I have done is make some changes to the Android kernel to increase the screen timeout to a sensible amount, let me know if you want to know how to do this.
I wasted a lot of time fooling around with this on my own, but nothing I tried seemed to work too well, so when you have some time, I’d like to know how you increased the screen timeout. This is really not urgent.
here you go David:
First of all you need to install something called adb (Android Debug Bridge) this is a command-line tool that lets you communicate with a device.
I suspect that, like me, you turned your screen saver to never to stop sleep mode - and I discovered that stops the screensaver but the stick will go to sleep with a black screen after 20/30 mins, not what I wanted!
I think that the issue is that normal apps can’t access system settings, only system apps , so you must use adb, from here: https://www.xda-developers.com/install-adb-windows-macos-linux/
CAUTION FROM HERE AT OWN RISK 
this approach does not require you to root the Firestick
remember to unzip the file before running the installer
then read this: https://www.technobuzz.net/how-to-install-adb-and-fastboot-on-windows/
command window, type “adb start-server” (a test)
then follows this guide on how to connect and disconnect to give you confidence: http://www.aftvnews.com/how-to-connect-to-a-fire-tv-or-fire-tv-stick-via-adb/
then for what we want: http://www.aftvnews.com/how-to-set-custom-sleep-or-screensaver-times-on-the-amazon-fire-tv-or-stick-without-root/
good luck, I have done this on 2 generations of Firesticks, wear your badge with pride 
Thanks for this. As part of my explorations, I had installed ADB, but I run into this issue (although everything in your documentation up to this point checks out):
Davids-iMac:~ orgel$ adb shell settings put secure sleep_timeout 123456789
error: device offline
Any thoughts about what might cause the device to show as “offline”? It seems like I’m connecting successfully prior to issuing the shell-settings command…
Davids-iMac:~ orgel$ adb connect 192.168.7.71
* daemon not running. starting it now on port 5037 *
* daemon started successfully *
connected to 192.168.7.71:5555Not wishing to state the obvious but have you checked that the Firestick ‘developer options’ that both are set to yes?
Other than that as you are using a Mac do you have anyone with a Windows PC that you could take your Firestick round to? Once set it is non volatile.
Always worth checking, but yes, the two developer options on the FireStick were set to yes.
I appreciate the suggestion, but (1) I’m not sure why macOS vs. Windows would make a difference in this situation, and (2) it’s against my religion. I’ll poke around some more, and maybe try connecting to the FireStick via USB rather than over the LAN.
If I discover anything worthwhile, I’ll post in this thread so that other Mac users can benefit.
[quote=“orgel, post:7, topic:63529”]
I appreciate the suggestion, but (1) I’m not sure why macOS vs. Windows would make a difference in this situation, and (2) it’s against my religion
[/quote]
seriously it’s not the OS but it will be a different binary for ADB so a possible issue on one version not the other? good luck!