Do you by any chance tried to play an HDR10+ file?
My N2 also exhibit same behavior as yours when trying to play HDR10+ with CoreELEC 9.2.0
Try checking the file with MediaInfo and see if it’s HDR10 or HDR10+
If it’s indeed HDR10+, download the latest nightly and it should play fine with HDR10.
If it’s HDR10, there might be other problem. The devs will need to see your logs to check it.