If you are using an USB-MIDI...
I'm using a professional firewire audio interface (Focusrite Saffire PRO 24 DSP), the midi ports and hardware working perfectly.
I also have a cheap Chinese USB-MIDI dongle but it will not transmit sysex no matter what.
Midi-OX will sometimes stop routing sysex completely, but when I use only FSMP with software cable or real hardware cable, all is perfectly fine.
Midi-OX will also sometimes skip a reset sysex from FSMP.
I did try the loopback test and all is working fine with my midi hardware, so the problem is not sending with Midi-OX, but only the routing part.
Midi-OX does something wrong to the sysex when it's transferring it from the input port to the output port (routing).
I can contact Midi-OX author about this but the latest version is so old I don't think he is interested in updating it at all.
I think I'll just stick to going from FSMP straight to the destination without splitting with Midi-OX.
Unless, you want to create a small multi-output splitter for FSMP, it'll be very useful.
Found a critical bug.
Change the output port (while playing !), click OK, and immediately double-click any song.
I think it's related to sysex delay again.