CFL bulb burnout damaging fitting?
Many times I have found the center conductor in the light socket has flattened out, lifting that tab away from the base with the power off will usually solve the problem. I have found some “electronic” lamps (not incandescent) do not have threads that are as long or a shoulder stops the lamp from being screwed in far enough. Lifting the tab will fix this also in many cases. Give lifting the tab a try.