Too many big files all in one go. Windows barfs. Essentially the copying took too long because you asked too much of the computer and the file locking was locked too long and set a flag off, the flag is a semaphore error.
The computer stuffed itself and choked on it. I saw the RAM memory here get progressively filled with a Cache in RAM. Then when filled the subsystem ground to a halt with a semaphore error.
I have a workaround; copy or transfer fewer files not one humongous block. Break it down into sets of blocks and send across the files one at a time, maybe a few at a time, but not never the lot.
References:
https://appuals.com/how-to-fix-the-semaphore-timeout-period-has-expired-0x80070079/