MacOS USB drive no longer auto-mounts

After many reboots and different attempts at resetting firmware and SMC, I tried one more time today to address the problem in recovery mode.

I was still trying to figure out why, even in recovery mode, I could not delete the Volumes/Andromeda directory. Even after turning of SIP within recovery mode.

What I did was mount the volume with the recover mode Disk Utility. In my case it was named "Kit - Data"

Then, I opened the recovery mode terminal and did

cd "/Volumes/Kit -Data/Volumes"
rm -rf Andromeda

That failed (as always) with "Operation not permitted" but I also tried:

echo test > test

And it also failed with the same error. I was thinking that the filesystem was somehow corrupted but then again First Aid did not find anything. So, finally I said to myself "what if the immutable flag was somehow set on a directory. However, "ls -O" was not showing it.

Anyway, just out of a fit of desperation, I tried this:

chflags noschg,nouchg "/Volumes/Kit - Data/Volumes"

After that I was able to delete the phantom mount points. After returning SIP to enabled and restarting into normal operation, USB drives once again mounted!

I don't know which of the flags were set or what was up with not seeing it before but this finally got the machine back into operation.

It is confusing as to how this ever happened. What caused the immutable flag to be set on the directory?

Anyway, if someone else has this problem, this was the solution. It may not have required the SIP change in recovery mode but that is the steps I was taking to try to get those phantom mount points deleted. Since things are working and I don't know what happened, I can't really work on what the minimum steps would be.

This shows the /Volumes with two different Andromeda folders but the USB device is not plugged in. The Timemachine folder is normal. (There is also the OS disk but I wanted to keep the image small - it is the next one as it is named after the machine)

Unfortunately, I may not have been clear - I have tried to repartition and reformat one of the drives (I thought I said that) but it did not help.

I can not even connect other drives via USB now - none mount and I have to manually mount them. Even after fresh reboots/etc. These exact same drives mount without problems on my 15-inch MacBookPro running the exact same version of MacOS.

At this point, I can not even do a TimeMachine backup as it will not mount correctly.

I have fully repartitioned, redefined, etc.

They are directly connected via a USB-C to USB-A connector (since they are USB-A 3.0 devices)

This has always worked. I have also tried it via my USB-C hub but to do the main tests, I removed everything from the chain, just in case.

I have also tried all of the 4 USB-C ports (just in case) - but no matter what, the MacOS will not mount it via Disk Utility GUI or the auto-mounter but if I use the terminal (bash for me, as I am an old engineer) I can mount it correctly using sudo diskutil mount -mountPoint /Volumes/Andromeda /dev/disk2s1

This works then as expected, reading and writing files as needed. In fact, the GUI and unmount it but never to mount it again.

The drive then plugged into another MacOS machine will work just fine and see the changes that were made.

I think something corrupted the MacOS automounter or mounting data deep inside as fstab and the mount tables look good and the core diskutil command line tool shows the correct thing.

I just don't know where to find the logs or telemetry for the automounter or the Disk Utility GUI mounting failures (other than what it shows). Things are just a bit too obscured (made for non-technical users)

When running Disk Utility from the terminal, I can see the following when it tries to mount:

2021-03-18 18:45:49.329 Disk Utility[1181:35003] Could not mount disk: Error Domain=com.apple.DiskManagement.disenter Code=49180 "(null)" UserInfo={DissenterPID=0, Target=disk2s1, Action=Mount, DissenterStatus=49180, Dissenter=true}

Oops, forgot to include the line in the console logs that follows the Disk Utility entry:

default	18:51:27.189052-0700	runningboardd	Invalidating assertion 158-101-647 (target:[anon<Disk Utility>(501):1181]) from originator [daemon<com.apple.coreservices.launchservicesd>:101]

This looks like it is some form of internal code assertion. Combined with the above error, something is not happy but it is not a problem when mounting by hand. It also continues to be a problem after a reboot and such.