It has been my experience that as alkaline cells near their end of life, they become intermittent. It appears to be an internal phenomenon as polishing the contacts doesn't help. I suspect it has to do with a high resistance developing around the nail in the center of the cell.
I have been using Guidesman high intensity flashlights for the past several years. I have six of them located in strategic places in home, office, shop, car, and boat.They are waterproof, focusable, and have outputs between 500 and 1500 lumens. To date, I have not experienced a switch problem. Should one occur, the switch is located in the end cap and It could easily be replaced.