Step 1: Notice that the listed symptoms form one recognisable pattern.
Excess spatter, a fiery unstable arc, flux coating breaking off, and porosity in the finished weld are not four unrelated problems, they are the classic combination that shows up together whenever one particular contaminant is present.
Step 2: Trace the effect of that contaminant through the arc.
If the electrode's flux coating has picked up moisture from the air, that trapped water turns to steam and then dissociates into hydrogen and oxygen gas the instant it reaches the extreme heat of the arc, and these gases expand violently.
Step 3: Follow the violent gas expansion to each symptom.
This sudden gas expansion disrupts the smooth transfer of molten droplets, giving a fiery, spattering arc, and the same steam pressure building up inside the coating can crack and flake it off. Meanwhile hydrogen dissolved in the molten pool has no time to escape before the weld freezes, so it gets trapped as porosity. Since a loose connection, low voltage or a faulty machine each produce very different, narrower symptoms, moisture absorbed by the electrode is the cause that ties this whole set of defects together.
\[ \boxed{\text{Moisture absorption by the electrode}} \]