The contact pins go through the board. The board has a metal pad where the pins go through. The solder joins the pin to the plate. On the RCM the pins begin to separate from the solder creating cracks around the pins. (could be from vibration or perhaps they were 'cold/ disturbed joints' from the factory?) These pins are square tube shaped and create straight line cracks around the pins. This makes a loose electrical connection. Resolder reconnects the pin to the pad.

ireland.jpg

https://learn.adafruit.com/adafruit-...ommon-problems