merging multiple midi tracks into one using send and receive

Hello,
I would like to send the midi notes from several midi tracks to one single midi track.
I am sending data from each midi track using midi devices like this:

and receiving with one midi device on one midi track:

After around 5 seconds of working great, the receiving device stops sending midi to its midiout. Even a simple "64 127" to the midiformat doesn't go through.
Suspecting a note off handling issue, I've tried to midiparse the data and use stripnote, makenote, and flush with something like this:

But it still breaks after 5 seconds or so.
Sometime notes get stuck like if they didn't receive their note off message, but flush doesn't help. Sometimes pitches are incorrect, as if the order [pitch, velocity] was broken by another [pitch, velocity] message arriving at the same time.

Is there a proper way of merging multiple note messages from different sources?
Or is it a limitation of send/receive objects in Max For Live?

any help would be greatly appreciated!
Florent