For whatever reason the sear and or trigger isn't resetting all the time. It could be something a simple as the trigger contacting the trigger guard or the sear lightly contacting the stock someplace. The sear could also be "pinching" on the trigger housing.

Strange that it works indoors but not outside. I doubt the temps in FL are cool enough to thicken any oil, but never say never. In this part of the world its a common problem this time of the year. Its just a guess, but I'll bet if you gave the rifle a smart whack with your hand while the bolt is open it will probably work every time!

BTW the safety can't be engaged when the bolt is the fired position, the safety bar is blocked by the bolt handle.

Bill