I needed to book some tickets via miles and was short because of 2 flights not booking after 1 week. I finally caved in and called them and got the miles booked during the phone call. Showed up same day. The call center agent was aware of problems with return flights sometimes not booking. My 2 missing credits were 2 one ways though.
Still waiting for a flight from this Sunday though but this time I am in no hurry. Just painful having to keep track on it yourself.
Apart from Frontier miles still not worth this much anyway. At least this time I just used 30k miles for a 1 way to Mexico during Thanksgiving week which would have cost 500$ without taxes.