Isn't it amazing that we continue to have socket issues after all of this time? Here we have untold dozens of quality manufacturers out there and yet so few seem to have found sockets that are trouble-free or will last as long as the fixtures. Some of the sockets out there are simply atrocious. Generally those that claim to be "universal" bipins (accept both G4 and G5.3 lamps) are the worst. Years ago I started to request T5 Wedge sockets in place of BiPins when ever possible.
One interesting correlation: It is often the case that those fixtures that have crappy sockets are also the easiest to change! Find yourself a source of good quality bipin sockets and buy a bunch... and be prepared to spend the 10 mins it takes to change out the poor ones when you are lamping the fixtures. As you do this, you will also discover that many of those crappy sockets are attached to the fixture lead wires with un-sealed, aluminum crimp connectors; offering you the opportunity to improve the internal connections as well. (or just buy better quality products
To give credit where it is due; I have found the BiPin sockets used by Auroralight, Hunza and BK to be the most trouble-free.