You might see a FAIL.TXT appear on your MICROBIT drive when you are flashing a .hex file via USB.
On the latest micro:bit (V2), this will be accompanied by an error displayed on the screen, such as 504
The FAIL.TXT will contain the error message and the type
error: The transfer timed out.
type: transient, user
- The make and model of the device you are using
- The Operating System and version
- The DETAILS.TXT file from your micro:bit
- A link to the editor you were using when this occurred eg makecode.microbit.org
- A copy of the .hex file or link to the program that caused the initial problem.
- The name of any anti-virus software you are running
Please also check that any anti-virus protection you have does not interfere with reading/writing data to USB drives and whether direct flashing from the browser with the apps and editors resolve the issue