Two big “ifs”

If you indeed have a system where the Ignitor doubles as the flame sensor,
and
If some of the tiny DC current is going astray due to a short circuit made by electrically conductive soot/dust/corrosion/cracked insulation
then:
changing air humidity will affect how much of the current goes astray

Higher Humidity = problem appears

Low Humidity = problem less likely

You are a braver man than I
if you take a tiny artist’s paint brush,
dampen it with distilled water,
and “paint” suspected trouble spots.

I would wait until warm weather,
or until I had borrowed enough portable electric heaters to keep the house warm.