So for some reason, it looks like mpv is not detecting the file format properly. The line that reads:
[demux] Trying demuxers for level=normal.
is then followed by:
[lavf] No format found
This should read something like:
[lavf] Found 'avi' ...
I don’t know why this might be happening. Did you install mpv and vlc using either pamac or pacman, or did you use another method? You could try forcing the format to see if the file at least then plays. I would also recommend using either systemd mount units (see Systemd mount any device and Systemd mount unit samples) or fstab (/etc/fstab) for permanent network share mounts.