Hello, the integrated circuits (chips) are atomic scale in size, wires are 8 to 10 atoms of gold wide, invisible without a microscope... all sorts of things can happen in the manufacture that can lead to intermittent failures later.
There are similar issues with the printed circuit cards the chips are mounted on, namely cold (delaminated) solder joints and cracks in the printed circuit 'wires'. As the printed circuit card warms and cools, these cracks open and close the circuits..... electrical arcs often form and will 'heal' such a crack for a while... then it will fail later.
These can be difficult or impossible to trouble shoot, as the voltage from the meter used for the test can cause an open circuit to arc and heal temporarily. Lets wait for the analyser software you ordered and see what comes up.
There can be similar problems with oxidized wire connections... all of this is is inexcusably complex in my book, but it is the world we are living in.
Regarding your payment, you paid Just Answer... but I only get paid from that amount from Just Answer IF I provide a an answer that you rate positively.
Stay in touch, let me know what you can discover, we can go from there without a time limit.