My Roku 3 has been rebooting a lot for the past couple months. It's connected via HDMI to an AV receiver, which in turn is connected via HDMI to the TV. A Harmony remote controls everything.
The reboots occur when the Harmony is used to turn on the system. More specifically, it turns on the receiver and the TV (the Roku is always on). The Roku then immediately reboots. It does not happen every time, but it does occur at least once a day.
This system configuration hasn't changed in over a year. The firmware on the receiver and TV has not been updated in over a year (it's up to date).
The most annoying part is that the Roku forgets it's display settings after the reboot. It changes from 1080p to Auto. That in itself would not be a problem, but then the next time the system is turned on the Roku senses the TV revolution to be 480p. Ugh!
Prior to a couple months ago, the auto display setting on the Roku worked fine (1080p).
I have contacted Roku technical support, but their responses have been slow so I decided to seek help here.
As far as the resolution goes, it's a known issue that Roku is working. For the reboots, I have no idea. But I have my Ultra and 4 both connected with CEC enabled and haven't noticed this happening. But I haven't watched for it either. Usually when the TV is first turned on, it's to watch broadcast TV, then the Roku is used later. It's certainly possible for it to reboot during that time without me noticing.
Dan Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.
I also have no idea why it reboots but one thing I'd try is to change the order things are booted up in the Harmony. Maybe try have the Home command sent to your Roku first to wake it, then the AVR, lastly your tv. Why I'm thinking this is that maybe its related to an hdcp handshake error. I love that the Harmony is so configurable.
I also suspect that the Harmony remote may be causing the reboots. Currently, it sets up the activity in the following order: 1. Turn on TV 2. Turn on AVR 3. Set AVR to HDMI3 4. Set TV to HDMI1 5. Send Home command to the Roku
I tried to change the order of the commands, but the Harmony configuration program on my PC won't let me move the Roku Home command (step #5) earlier in the sequence. In fact, it won't let me insert any commands until step #5. Annoying!
So instead I have inserted a one second delay before Home command is sent to the Roku. We'll see if that helps.
If the changes on the Harmony don't work, and you have an sd card in your Roku, you might try removing the card, unplugging for 30 seconds and plugging in again, that's always solved the reboot problem on my Roku 3 which occurs every few months. I also format the sd card on my laptop before putting it back into the Roku (which then formats it again).
I finally found a fix to the problem. The one second delay that I inserted did not make any difference. However, I changed an HDMI setting and now the system no longer reboots when I turn on the TV & receiver.
At this moment, I can't remember what HDMI setting I changed to fix the problem (it's been a week since I made the change). I can figure it out again if someone needs the details.