Plague Harvester mobs - skill registration issues

I've noticed some difficulty in registering hits with Lightning conduit against Plague Harvesters (those big flyng bugs resembling an overgrown mosquito :D ). It looks like the spell is not registering at all against them. This is somehow mitigated if the player characheter is standing on higher ground compared to the mob.
I can't seem to understand whether it's the spell not doing all the damage on the mob or failing to applying the multipliers from shocked ground/conductivity curse and therefore only dealing the base damage.

For reference I'm running Ball Lightning/Lighting Warp for general mob cleaning, with Lightning Conduit both on CoF and casted. Both versions of this spell don't seem to work correctly against the mob. (only tested in maps.)