Strange problem/bug sending midi sysex

Hi, I see a strange problem/bug with self._send_midi().
I use this code to send out parameter values to display on a iPad:

This is just an example for parameter 14.

Listener: self.song().appointed_device.parameters[14].add_value_listener OR turning knob 14 on the MIDI Fighter Twister

Action:
parNr = 14
header = (240, 126, 3,)
devPar = (parNr,)
val = tuple([ord(c) for c in self.song().appointed_device.parameters[parNr].str_for_value(self.song().appointed_device.parameters[parNr].value)],)
closer = (247,)

sysexMsg = header + devPar + val + closer

self._send_midi(sysexMsg)

self.log_message("csslog: " + str(sysexMsg))

I always get the correct output in the css log and I get midi sysex output:

1. after loading a live set and in the first selected track there is a selected/bluehanded device
2. when I click a random parameter in a selected/bluehanded device > in this case not only the now selected parameter works but also every other parameter of this device...

But there is no midi sysex output when:
1. selecting (blue hand) a device with a midi controller input
2. selecting (blue hand) a device by mouse clicking on the device menu bar
3. selecting (blue hand) a device with keyboard arrows left/right

I also tried to use "selected device" rather than "appointed device" but that also doesn't work.

Any hints what might be wrong with the code ?

Regards, mj