Hi @tele_player. Stuck notes can be due to a variety of reasons but a properly built Zynth with approved parts does not suffer from these.
Poor MIDI interface design / components can lead to MIDI messages being lost. This is not what you are experiencing because you are using USB MIDI. (I found that the unorthodox MIDI interface used in Zynthian works much better than the more traditional interface I had previously built.)
Poor USB interface. Zynthian uses standard Linux USB class compliant drivers for MIDI USB devices so if the device works well with other operating systems without bespoke drivers it should work fine with Zynthian. Some cheap USB MIDI interfaces omit the opto-coupling which tends to work on very few devices. You don’t seem to be suffering this issue because you are using a class compliant USB device (Arturia Minilab).
If the Raspberry Pi is struggling to compute synthesis output then it may start to behave erratically. Zynthian includes many synthesis engines, some of which are resource hungry and can driver the RPi to resource exhaustion. (We are looking to minimise or eradicate this but don’t want to limit the device’s versatility.) If you are using a particularly resource hungry configuration of synthesis engines then it is plausible you are suffering such behaviour. Let us know what Layers, etc. you have configured when this occurs.
If the Linux kernel is hanging due to hardware issues then it could result in failure to service other services including MIDI, synthesis, etc. A poorly designed audio driver or audio interface could result in such behaviour. I am not familiar with the Audioengine A2+ speakers so don’t know if they would cause such an issue but it is plausible. They look to be class compliant USB audio devices so should work okay!
The bottom line is that it is certainly not normal for zynthian to hang notes and if this is occurring with a particular configuration we would like to resolve it (which may mean documenting a constraint).