I tried downloading a PPV from TrillerTV today that I purchased and nothing worked properly. I even tried the MP4 and both MKV options and it fails once muxing. I've attached the log.
fanatic
click settings in the upper right hand corner of the streamfab interface,
click preferences - under VIP services - choose preferred settings - under video format choose MKV (MKV Toolnix)
click ok, restart streamfab and retry you movie again and see if it still fails on muxing.