Interesting post IDX. First, good effort; willing to work in the cold, and punch through the frozen topsoil. Second, VERY nice late season silver digs! Third, good observations and write-up to discuss it. I don't have much cold weather hunting experience, but have had hunts with similar poor detecting capabilities; compared to normal days. I suspect multiple things are happening to produce these problems.
Couple thoughts: External forces like EMI, solar flares, partially frozen ground, etc. are usually beyond our control. Understanding them doesn't seem as important as understanding our detectors. With our current machines, there are only so many adjustments we can control, so work with what you got. Trial and error may produce improvements, and may even give clues about the unknown forces. Other creative solutions can help too; like using plastic bags and hand warmers, and tinfoil hats.
"Lord, grant me the serenity to accept the things I cannot change, the courage to change the things I can, and the wisdom to know the difference"
Then there is next level thinking: Understanding the roots of the problems, so we can create new solutions, like a new, improved EMI filter, solar flair blocker, gold isolator circuitry, or a cold weather program for my Nox. I hope you tap into the right group of minds on this level. I see the gears turning...