Midibuffer:addevent malfunction - solved: MIDI Monitor app is broken

I’ve got a strange problem:
addevent() creates random garbage if I add more than 1 midi event per Frame.
Is this a known bug or maybe related to M1?
I allways just kept the sampleNumber at 0, but I also tried giving them oredered numbered and limiting the number of events. I also added clear() to make sure the buffer is in a predictable state. Also tested with complete static midi events to add, so it is not a broken event in any way.
It all doesnt help: my addevent() can not handle more than 1 event here…

I monitor the midi via a normal Apple virtual midi bus and the “MIDI Monitor” app.

update: I have updated macos to 11.4 and xcode to the lastest version 12.5.1
recompiled it all (pluginhost included), but the problem is still there.
My work is in a vst3, and I ouput the midi to the midoutput in the in the pluginhost, then via IAC midi to the MIDI monitor app.

The MIDI Monitor app seems to be the one that garbles the midi…
MidiPIpe shows the correct data…