I haven't had any problems with my Duncans i bought last year.
Pickups are pretty simple devices. But given the fragility of the coils and the conditions they're played under most of the time, i'm amazed at how durable they can be.
The problems you've had with your Invaders may be an internal quality problem, or it could be as simple as
Seymour Duncan getting a bad batch of wire from a supplier. If one of the tiny coil wires breaks, the pickup is junk. Since all the problems you've been having are specifically with the Invader model, my guess is that there's some kind of materials defect that is affecting a particular batch of them.