Recording iOS Simulator produces empty files

There was a timing bug in video recording that could result in 0-byte files on some systems. I'm sorry, but there is unfortunately no workaround. This should be addressed with changes in Xcode 10 Beta 3+.

I had that same issue and was scratching my head over that for days. The fix turns out to be simple though. Make sure you press Control + C and quit the simulator. Once you quit the simulator it starts to actually produce the recording.