I don't know if that's what happened in this case, but it could just be a computer glitch. If the computer catches a changed address, misspelled name etc. they put the names into a hold file.

This is not necessarily nefarious, but your friend needs to get his/her name back on the voter list. They can probably go online and re-enroll. There's still time before November, but don't wait too long.

Some states do purges of voter rolls and eliminate voters that haven’t voted for a long time because it’s assumed you’ve either moved or died.

and as usual by the time we get the whole voter suppression story for this election, the results will be certified and nothing will be done to remedy the situation for next time.