Why will LED bulbs not work in candlabra light fixtures where incandescent was working fine immediately prior to putting in LED. In some cases I can screw down until I'm afraid of breaking bulb and it will work. In others, I screw 1/2 way in and can jiggle the bulb around and it will light when I hold it cocked to one side.
I can see two reasons.
One is that the shape of LEDs near the bottom is often fatter than an incandescent light. Sometimes this doesn't allow them to screw down far enough.
The other is if your fixture has a dimmer. Some dimmers do not "play nice" with LEDs. If this is the problem, putting one incandescent back in will often make the dimmer work again, though the LEDs may not dim well.