Blank screen after reboot for some video modes

I’ve had a problem with the N2+ and the latest core ELEC sometimes showing a black screen after a reboot. The Hard Kernel splash screen displays OK, but coreELEC boots to a black screen. The OS is still running fine. I can SSH in just fine. If I unplug and replug the HDMI cable, the display comes back. This seems to depend on the display mode. Some modes do this after reboot, some do not.

I asked about this on the Hard Kernel forum, since they fixed a similar issue in Petit Boot, and they indicated that this may need to be addressed in the OS as well. See here:

This problem reliably occurs for me with 4k@30Hz, and 4k@23.976Hz. It does not happen as often for me with 4k@60Hz, but 23.976Hz is obviously a mode that gets a lot of movie use.

Why would you set your GUI to 24P before restarting? You should let CE automatically switch resolution and refresh rate to match the content. Leave GUI at 1080P.
I’d bet this is a HDMI cable issue, rather than CoreELEC issue.

The resolutions you mention, and all other chosen in “Settings-System” panel, are ONLY used for GUI. When Kodi is properly set in “Settings-Player” panel ALL movies will play at their native resolution/refresh rate.
So the advice is: always set 1080p at 60/50 in System panel, and in Player panel set Change Refresh Rate at “Start-Stop”.
This will always keep your GUI resolution at 1080p at 60/50, and play all movies as they should, at their native resolution and refresh rate.

I’m thankful for the work around, but it’s not a solution - the bug persists. Also, I’ve noticed a tendency for the UI to stick to refresh rate previously played when refresh rate changes for playback but resolution does not, which compounds the problem if you set the UI to a 4k mode. I haven’t noticed a similarity for it to stick to the previously used resolution, so setting the UI to a 1080p mode should help as a work around.

This is not a cable issue. The issue persists with multiple cables and multiple screen. Per the referenced thread from HardKernel and their recently patched PetitBoot, this appears to have been a known problem that they recently worked on. I don’t know what went into the patches, but HK’s release of PetitBoot 20201020 addressed black display issues.

Setting the UI to 1080 is great. Thanks for that tip. It seems to help. But, the underlying bug is there.

And did you update petitboot?

Yes, I updated petitboot. The HardKernel team recommended I should share the issue with the OS team

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