sendMIDI occasionally fails to actually send syses midi bytes, while exiting successfully

[xot]

I use sendMIDI in an Ableton remote control script for the Electra One (see https://github.com/xot/ElectraOne) to bypass the slow sending of long SysEx dumps within Ableton itself. But occasionally a call to sendMIDI like

sendmidi dev 'Electra Controller Electra Port 1' syx 0 33 69 ...

will return with exit code 0 (i.e success), while not actually sending any MIDI bytes out to the port (as reported by MIDI Monitor). Have you or anybody else ever seen this behaviour too, or could you perhaps give an explanation?