Hello, I post it here as it seems to me the most promising thread :) . Well, the fact is that GarageBand definitelly misses midi events, or at least ir seems to me. In the beginning I thought it was an electrical issue, because unplugging the computer and the keyboard from the mixing board worked. But still there was the stuck notes issue (plus de sustain pedal issue, which I have left aside). As reported by Midi Monitor ( https://www.snoize.com/MIDIMonitor/ ) , the note off events are arriving. But GarageBand ignores some of them. Furthermore, depending the sound choosen, Garageband ignores more or less of these events. I am looking for some kind of sampling over midi events parameter. But I don't discard that it is a GarageBand bug, as shown in this other post: https://apple.stackexchange.com/questions/113112/stuck-notes-with-a-midi-controller-and-garageband-10-0-1 Any advice is welcome. Thanks.

Thank you for your response. I have been testing since your answer. I will number the questions, if you do not mind. 1. It is connected to a 5-pin to USB converter directly to a USB port. 2. No, I have not. 3. No , but I am testing simultaneously with Midi Monitor. 4. No. No load. Ok. Here are my results. Midi seems to be very sensitive to electrical issues. Thus simply plugging my Mac Book Air to the adapter, or plugging the Mac to the mixing board makes noise midi event to appear. But, in a stable configuration, here it is what it happens. By some strange reason, press events appear on channel 4, but release events appear on channel 1. I don't know if it is due to my Roland Em-10 keyboard or the 5-pin to USB converter, probably the first. By the way, it happens only if between both events little time passes. For example, if more than a second passes, press and release appear on same channel. Behavior gets more complicated when several keys are pressed (usually if little time passed all events appear on channel 1). For some strange reasons (again) GB interprets this channel anomaly differently depending on the sound selected. For example, for Orchestral - chorus - ... release event is interpreted correctly, though channel is different. But for others the release event is ignored, keeping the sound. I am not a midi expert, but I think that press and release should be on the same channel, it seems intuitive to me. So it may not be a GB issue. What really confused me is that the keyboard (cmd+k) behaves correctly with release event on different channel (i.e. it shows the key released). I will go on trying, but any comments are welcome.

Thank you very much for your answer. I will try a reset.

I've done a fatory reset. And everything remains the same. The midi channel anomaly could be electrical issues. I've got to try with another midi conversor. Thanks for yout help.