I think it’s most likely the PCM audio in the french version. This should be easy enough to fix. Someone might have a faster method, but what I would do (given that I already have the programs, which are all free):
Demux the audio track with tsmuxerGUI. Import it into audacity. Export ac3. Use MKVMerge to build a new MKV. Drag in your old one as well as your new ac3 audio. Unclick the PCM audio and rebuild the MKV.