Client is not compatible and server is not sending a compatible format

[Stroller]

That last log is meaningless.  There is a check box in Dashboard > Logs to turn it off because it is so useless.

As far as I can tell, both files are effectively the same in terms of codecs and color depth, etc.

Yes but the audio is different so maybe ?
It show this error on subtitles which I don't find in the files that works : 

Code:

[matroska,webm @ 0x55f2ad692600] Stream #9: not enough frames to estimate rate; consider increasing probesize

[matroska,webm @ 0x55f2ad692600] Could not find codec parameters for stream 7 (Subtitle: hdmv_pgs_subtitle (pgssub)): unspecified size