... Out of 1726 in the field for <2 years, 78 have had intermittent connections and were replaced. The application is not challenging, clean, dry, low vibration, low stress and no movement...
I use 3M twisted pair ribbon cable with Harting IDC DIN41612 connectors (64-way), in test jigs. The combination has proven reliable, but there is a fault that
can occur during initial cable assembly.
The cable can sometimes have a distorted conductor-to-conductor pitch, so that it doesn't line up exactly with the IDC connector tines.
If the misalignment is bad enough, it results in adjacent conductor short-circuits.
Conceivably, if the misalignment is not that bad, but still present, it could lead to unreliable conductor-to-tine contacts; contacts that are not
gas-tight and that will fail over time.
To guard against this, I check the cable alignment against the IDC before assembly, then check for continuity and no adjacent shorts after.
Sometimes I do have to massage (stretch or compress) the ribbon cable into good alignment, beforehand.