I’ve been having the same issue with LibreELEC 9.0.0 on an ODROID C2 connected to a Sony HT-XT1 sound base. Had no worries with 8.x at all playing anything really (DD, DTS, DTS-HD, TrueHD, AAC, MP3), using HDMI passthrough for all supported formats. AAC is now only playing when I change output to 5.1 and enable stereo upmix, and the sound output will typically become “corrupted” (deep and slow) after playing a video. Passthrough stuff is still fine though. If anyone has any ideas I’d appreciate them!