I might suggest a layer-by-layer XOR of the bad
channel vs the good. Do not know whether PCB
DRC tools can do this but it's a common debug /
verification thing to do in IC layouts. If possible
use a "blowback" database from the PCB mfr.
This could turn up some routing difference -
either intentional (which would be in your DB)
or accidental (spot on PCB house photomask
becomes via / line break.
For that matter an X-ray inspection facility
could produce you an all-layers image which
I'd bet someone could do a pattern recognition
difference on - maybe a MIL grade PCB outfit
or one that does any aerospace grade work,
would either already have this in house or
tell you who they use.
I do notice offhand that the problem channel,
unlike the rest, has its cyan trace (function = ?)
making a 3/4 loop over its own circuitry - the
others are more straight and more random.
Maybe this is your "magnetic pickup". Might
cut and peel (if you're lucky enough that cyan
is a topside or bottom side layer) and mag-wire
direct, see what changes. If not, maybe find a
lucky drill-point that takes out only that trace.
Although the two on the left are kinda weird
loop antennas too... kooky routing, why the
matchy-matchy line lengths (only reason that
comes to mind) for sub-MHz stuff when it's
1nS/foot? The bad boy, though, has the largest
loop area.
Any chance that the problem is documentary -
like the component install drawing or silkscreen
has an electrolytic cap or a diode reverse-placed?