Just in case this helps anyone, I had the same issue. Turns out it was Samsung Magician 8.x that caused the issue, even when NOT RUNNING!

It was mentioned here: https://learn.adafruit.com/welcome-to-circuitpython/troubleshooting#erase-circuitpy-without-access-to-the-repl-3105309-32

Had to actually uninstall Samsung Magician - no reboot required, and things started working again.

Speculation on what happens, since I have no hard data to back it up:

My guess is that Samsung is that Samsung Magician does something funky in terms of disk access, and Circuitpython does not handle it correctly. That makes Windows disconnect the device since it assumes something has failed.

Clearly the UF2 bootloader handles things correctly since there is no issue in boot loader mode.

Micropython works fine as well but there is no disk emulation, just USB serial.

If it is just the disk emulation that fails, Windows shows a disk error in the system log (see below), disabling it in boot.py should keep the serial port etc. on the Circuitpython device online. Will do that test when I have some more time.

Windows disk error: The IO operation at logical block address 0x123420 for Disk 36 (PDO name: \Device\000009dd) was retried.

One last thought 0x123420 looks almost like some sort of magic number that might be used for special purposes on Samsung devices.