Mulatto,
i have on occasion had issues with UA ticketing it once i made the reservation off the app, 3x iirc....i was told by a 1k res agent that shares sometimes acts up and will take longer than usual to ticket, the one time i did call she had to call the "help desk" to get it to push thru to a actual eticket, normally have corporate travel book it but it has happened to me as well, more times than not i've had no real issues.