It appears that there is a problem with Mac Nomad Pixel Map Movie files.
Stock Layer file (Lib 0, FIP 112) is a good place to see the problem.
Select Layer file, Loop Forward with a speed. "Loop Reverse" does nothing. Also, when you have "Loop Reverse" selected already , and choose a file, it can sometimes simply "play" a still frame causing confusion.
2015 MBP Mojave 6K Nomad 2.8.2
When tested on a Gio @5, the "Loop Reverse" function behaves.
Thanks,
Matt