Case of defected PCB
There are two pieces of PCB fabricated from the factory , one is bad , the other one is good .How is the issue come to happen ? let's see below : 
Good PCB

Defected PCB 

After companring them , do you notice any difference ? Yes , in the  first picture , the connection is broken , 

How is that happen ? 
Let's have a view on the original gerber file , 

In the PCB factory , the enginners use Genesis 2000 to modify your gerber file . The engineer runs Genesis with function edited in C++ language . Some of them don't check the gerber file after modified by Genesis by accident .At this time , Genesis may possible to cut some connection because of the default action ( gap <2mil will be filled with copper or be broken ), then the bad production gerber file will be deliveried to production , 

The engineer from the factory tell us , they pay more attention to the gap , some gap has to be filled , some gap has to be broken .How do they judge " filling " or " broken " ? 
Sometimes , they analasis the circuit net by their experience , if the gap don't have any fuction , they will fill with copper or broken ; sometimes they rely on Genesis to fill copper or broke them .Mostly , they will compare the production file with original file in case too much difference on the production file . Unfortunately , there are 1-2% possibility that some production files are failed to be compared , and resultant with bad PCB . 

I kindly suggest the one who do PCB layout , better have a strengthen view on your circuit gap . We also will ask our engineer to be more careful with it .