Had your circuit been protected with an arc fault (not the GFCI), it would have tripped. As I read the responses from you and other folks, it sounded like an intermittent disconnect along the line somewhere. DANGEROUS.
Re-twist the nuts and tape them off. I would check others laong the circuit to make sure there are no more loose connections. The electrician probably got sloppy or tired when the house was built. If the wires gague can handle it, you might consider a 20A breaker on the line too. Sounds like you potentially have a lot going on!
Now, get off the computer and get back to work on the deck .......