SOLVED: Transcoding fails for some clients

[DazzlingTap2]

According to your logs, the failed transcode specify you're trying to encode into AV1 which is not supported by your iGPU.

Code:

Stream mapping:
  Stream #0:0 -> #0:0 (hevc (hevc_qsv) -> av1 (av1_qsv))
  Stream #0:1 -> #0:1 (ac3 (native) -> aac (native))
Press [q] to stop, [?] for help

Meanwhile the transcode is successful on Android because it is encoding into H264.

Code:

Stream mapping:
  Stream #0:0 -> #0:0 (hevc (hevc_qsv) -> h264 (h264_qsv))
  Stream #0:1 -> #0:1 (ac3 (native) -> aac (native))
Press [q] to stop, [?] for help

You'll need to reconfigure your transcode settings, go back to Playback -> Transcoding and scroll to Encoding format options and unselect Allow encoding to AV1. I do not know if you're still able to encode to AV1 without hardware acceleration.