macOS I/O is stuck when plugging USB hard drive, although one partition mounts successfully

Hello folks,

I'm curious to read any take on the following behavior from macOS which I can't explain.

I used an external USB drive (WD Elements 1TB) successfully for various months on my MBA M1 2020, hosting 2 partitions on it:

1) a DATA partition (FAT) of some 50 GB

2) a Time Machine partition (APFS encrypted) for Time Machine

As the disk is connected to my USB-C display, it happened several times that I unplugged my computer without un-mounting the drive.

What's happening now is the following:

1. I plug-in the USB drive
2. the DATA partition is mounted. It doesn't show in finder, but I can successfully `cd /Volumes/DATA` and read files from it.
3. I/O on the rest of the system gets stuck. I can use open applications, e.g. open new Tabs and loads websites in safari. But I can neither start applications (they just keep bouncing endlessly in the Dock), now launch binaries from the Terminal.

What's also interesting:

• There's no trace of a problem of any sort neither in /var/log/system.log nor in any group of Console.app
• The Disk Utility application does not list the physical drive, despite the DATA partition from it having been mounted.
• The Disk Utility application actually becomes unresponsive after a few seconds – plain operations like selecting Drive entries from my MacBook internal drives also don't work.
• Running `diskutil list` from the terminal also gets stuck.
• As soon as the USB drive is unplugged from the Mac, macOS becomes immediately operational normally. Apps that kept bouncing in the Dock without opening minutes long immediately open.
• Plugging the drive into a Windows computer is no problem. The DATA partition shows up normally and the rest of the system keeps operating normally.

Any hint?

cheers

michele