MIDI settings reset after MIDIServer restarts (macOS 27)
If you have created a configuration in Audio MIDI Setup and a connected USB MIDI device reports a port name containing a NUL character, macOS 27 cannot save the configuration. IAC buses you added and other changes disappear when MIDIServer restarts.
unplug that device and create a new configuration in Audio MIDI Setup. Details: Why do MIDI settings reset after a restart on macOS 27?
MIDI stops after MIDIServer quits (macOS)
When MIDIServer quits or crashes, apps that were already running lose their connection to it and usually stay disconnected. Input stops arriving, and output appears to be sent but does not reach the device. macOS gives no notice. This is not specific to one macOS version. MIDIFabric detects this within about a second and shows a dialog.
quit and reopen MIDIFabric. Other music apps that were running may need to be restarted too, and so does Audio MIDI Setup. Details: Why does MIDI suddenly stop working in a Mac music app?
MIDI-CI through the Mac may not work
If two MIDI-CI devices are connected to the Mac by USB and routed to each other inside the Mac, with MIDIFabric or another app, Property Exchange may not work, or may stop working after you power-cycle one of the devices (seen with Korg Keystage and opsix module). We have confirmed that macOS itself also exchanges MIDI-CI messages with USB devices, but the cause is still under investigation.
connect the two devices directly with MIDI (DIN) cables. MIDI-CI worked with this connection. Details: Why doesn't MIDI-CI work between two USB devices connected through a Mac?
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