I came across this last week. I was copying files to a BBC micro:bit V1 and it then stopped working. I found a
FAIL.TXT file on the micro:bit drive with content of
error: The hex file cannot be decoded. Checksum calculation failure occurred.
type: transient, user
It’s a bug which manifests in a few other ways and one that’s due to be fixed RSN apparently according to the description of it on micro:bit Help & Support: Error transferring file to the micro:bit since Windows update in February 2023. WebUSB is unaffected, hence a decent workaround.
I thought I’d mention it here to raise awareness as it’s confusing when it works for a while then appears to stop working.