This is 100% the sockets, and fixing it sux

Entire strings going out might be a different cause, I am talking about the flickering of lights under the inlane guides (primarily) and slings.
The sockets under the inlane guides are different, as they are meant to mount fairly flush, and are stapled in.
I have removed flipper plates, remove the insulating paper, pry off the staples holding the sockets (I pitch the paper, as I can't install new staples), remove wires, I then clean all the solder off the lugs, and flatten them, now the fix...
I file the barrel of the socket a little bit, at the bottom along where the lug is, I then add solder, joining the lug and the barrel. I think they are only pressed together, and that's the problem.
Now, I actually drill a small pilot hole and reattach the socket to the PF with a small stainless screw, the normal ones break.
Reattach the wires, and I simply put electrical tape over it all when done (a couple pieces, cross cross) to keep potential shorts from happening.
Then put the flipper plate back on, and check for clearance of the sockets and wiring.
Pain in the ass, but rock solid lights after that.
I also throw a dab of solder on the center of the bottom gold part to the other lug, for good measure.
Ymmv, but works for me on several route machines that had issues.
If you don't understand this whole description, or aren't comfortable doing all this, don't do it! (Or do so at your own risk)

Also of note, this is not limited to Spike, I have done the same on a few SAM games too.
Also, I have heard rumor that Stern is addressing this issue, I certainly hope so.
But it is nice after they are fixed, to see all those lights working every time.