CoreMIDI and "midiserver" fail to load after update to MacOS 15.5

I am reporting a MIDI-breaking bug on my 2018 MacBook Pro (2.3 GHz Quad-Core Intel Core i5) that appeared immediately following the update to macOS 15.5 from a previous version of Sequoia, which was either 15.3 or 15.4 - I can't remember exactly.

My system was fully functional before the update, and based on the previous version of MacOS 15 Sequoia. I had not installed any new MIDI drivers, and no other software or hardware changes were made to my system. The OS update was the only variable. After the machine rebooted with 15.5, Logic Pro would hang on launch and present the error, "Error initializing CoreMIDI." This immediately stopped all music production. Since MIDI based music production is the primary function of this machine, this is a system breaking bug in my case.

To see if the issue was system-wide, I then tried to open another DAW, Reason 13. It also failed to load properly, giving the specific error, "Failed to open MIDI support library - Please restart your computer and try again." This confirmed the problem was with CoreMIDI itself. When I attempted to diagnose this using the Audio MIDI Setup utility, the application would hang indefinitely as soon as I tried to open the MIDI Studio window, requiring a force quit.

I began troubleshooting by shutting down and disconnecting all external peripherals to rule out a device conflict. This made no difference. I then deleted the com.apple.audio.AudioMIDISetup.plist preferences file to reset the MIDI configuration, but the errors in all applications persisted exactly as before.

With standard fixes exhausted, I proceeded with a full reinstallation of the operating system. I booted into Recovery Mode and used the internet to reinstall MacOS 15.5.

After reinstalling 15.5, the fundamental problem persists. The behavior is now slightly different, but the main problem that CoreMIDI fails to load remains the same. When I open Audio MIDI Setup and select MIDI Studio, it no longer hangs indefinitely but instead hangs for maybe 60 seconds, then throws another error message:

"The MIDI Server can't be opened

Audio MIDI Setup couldn't open the MIDI Server so you can't view or edit your MIDI configurations. If you recently installed a new MIDI driver, try uninstalling it and then open Audio MIDI Setup again. If Audio MIDI Setup works correctly after that, contact the driver's manufacturer for further support."

To reiterate and clarify, I have not changed any software, hardware, or configurations, including MIDI drivers, other than the update to MacOS 15.5.

From what I can tell, the com.apple.midiserver process in macOS 15.5 is failing to launch on my hardware. Since the failure occurs on a clean installation with no peripherals attached, to me that suggest a core bug in macOS 15.5 itself.

Having my backups in place etc., my plan for now is to wipe my boot NVME and do a completely fresh reinstall of an earlier version of Sequoia, hopefully 15.3 if it's available.

Am I missing something?