With zero stealth defense, 15 melee defense, 16 etheric defense, and Lightning in Your Veins active (2 reactive defense), the rail serpents' lightning lunges did 1-2 damage to me. The modified Lightning Lunge must be 1 base damage untyped or 5 or less base damage melee damage.
Also, Clashing Blow did not trigger against the serpents' Lightning Lunge, but Shark Bite did. However, Kinak has stated that techniques that are dependent on what technique the opponent is using only look at the base, as-written form of the technique, in this case Stealth. Meaning this does not rule out Lightning Lunge being untyped or melee.
A third, much less likely explanation is that modified Lightning Lunge is still stealth, but has negative base power (on the order of -7). Of course, this seems absurd and has no precedent.