What format did you get it in, and what container are you trying to mux it to in the end?
I grabbed the mkv in multi parts though jdownloader. I had to unzip with 7zip because winrar was giving me an error. I tried to tsmux into an iso but got the error so then I got an old version of mkvmerge to recreate the mkv to see if that would fix the problem but it didn’t.