Random MIDI note bursts in MainStage on MacBook Pro M1

I'm experiencing a nasty problem with random Midi note bursts in MainStage.

It looks and sounds like hundreds of Midi notes are being sent all at once and it won't stop until I force quit MainStage.

The concerts generally works fine. I use patches with 1-6 EXS Sampler Instruments and 1-3 playback plugins running a click track and some backing tracks. A huge amount of 3rd party AU plugins is installed on the computer, but I exclusively use Apple plugins in MainStage. Very basic, occasionally an EQ or compressor, in most patches no additional plugins at all.

A Yamaha 88 keyboard is connected via Midi (not USB) to the Interface (Presonus Quantum 2626 TB3) which is set as both audio I/O and Midi input device in MainStage.

Even using the "panic" function (which I assigned to a controller) doesn't help, there is no way to stop the continuous Midi note events - without touching the keyboard. It has only happened while playing.

The problem is totally random, it happens with different patches and sometimes MainStage just works fine for 3-4 hours.

I am an experienced MainStage user since 2010 with +1k gigs on a very old MacBook setup with ZERO problems. This "new" setup with the M1 MacBook Pro and the Quantum is unusable atm.

Any help or hints where to look at is highly appreciated!

[Re-Titled by Moderator]

Original Title: random midi bursts