[FFmpeg-user] distorted audio in concatenated mkv

[lejeczek]

Hi guys.

I have two mkv files which on their own playback fine but 
when I concatenate them then that second file's audio is 
pretty distorted.
In case it might matter, I see as 'concat' works:
...
[matroska @ 0x558ab61d6180] Non-monotonous DTS in output 
stream 0:1; previous: 986790, current: 986784; changing to 
986790. This may result in incorrect timestamps in the 
output file.
...

Is there a way to fix this weird problem?
many thanks, L.