To be fair, repeat once means repeat once. That's exactly what it says and so its what the setting does. It might help if they added a note in smaller text like they do for other settings.
It does. But is much less natural than "alert twice" which would mean the same thing.
I think the problem is that they moved that setting. It used to be in the Sounds section where you would turn the alert on and off all together and then repeating was in a different context.