LibreELEC 9.0.1
Odroid_C2.arm
Four-channel FLAC, 24bit/96kHz with WAVEFORMATEXTENSIBLE_CHANNEL_MASK=0x0603 (FL-FR-SL-SR) is playing at what appears to be half-speed and as 2.0 stereo.
Running the file through SoX remix to add empty FC and LFE channels then changing WAVEFORMATEXTENSIBLE_CHANNEL_MASK to 0x060F (FL-FR-C-LFE-SL-SR) creates a file that plays correctly.
Both files play correctly in LibreELEC 8.2.5/Odroid_C2.aarch64.