MKV fast forward

Hello,

I have a sony bdp-s590, lovely machine, and great IQ. My only hiccup is that I am running into quite a few MKV files that do not let me fast forward or rewind when streaming with serviio. I've tried running the select files through MKVMERGE GUI, but to no avail.

Can anyone give some insight of what I need to do different?

Thanks

Do they FF/RW through USB? I've had some like this too, just don't FF/RW (unless they are remuxed to m2ts)