To answer your question, there is not a type of socket made that has never failed, and intermittant is one common failure mode for any socket.
SOme tubes have slightly fatter pins than other, and once shoved into a socket, they can spread the female elements some, loosening their grip. This alone is enough to cause intermitancies. The material of the socket housing has absolutely nothing to do with the metal contact pins. All the material does is hold them in place. I certainly will not be dragged into some esoteric discussion of tone of sockets, but the FUNCTION of the socket is to make contact with the tube pins, and THAT will not be affected by the material.
Pins can oxidize and make poor contact, likewise tube pins can oxidize and work poorly in sockets. Bent or angled pins can also spread the female pins and loosen them. SOlder to the circuit board or to wires can fail or crack, causing such troubles.