The problem most likely isn't locktite.... It's the fact that these screws were installed in winter when it was cold. Now that it is warm where he is the metal is a nanometer or so bigger and stuck. Heat would make it tighter unless yo heated the metal insert in the board and cooled the screw. Heating the insert would fuck up the setting of it. Don't heat the screw or insert. If anything you should cool it down in a deep freeze or by setting it out on the porch over night when it's cold out. I live in the mountains so remember tha cold to me is under 10F.
This is why bolts come loose on the mountain too, aside from the lateral force. If the screws were tightened inside your 75 degree house then taken outside, they are now not set.... This allows the lateral force to pull and loosen the screws. I typically tighten my screws on my porch and never have to screw with them again..... They are stupid tight if I try to remove them in the spring/summer. Proper driver head helps to prevent stripping the heads when tight.