The unique sword, “Apogee of Light” is phoning in it’s abilities.
“When a minion dies you gain a stack of frozen vengeance” does not trigger from the summoned weapons via ‘Forge Strike’ on Forge Guard.
This was tested with and without the ‘Shrapnel’ node. It does however trigger if you resummon the ‘Manifest Armor’.
Was also tested on Necromancer. Summoned skeletons that the Wraithlord zapped would trigger the effect.
Hitting with a melee attack does consume ‘Frozen Vengeance’ and gives the frenzy buff to the Wraithlord and his buddies. It does however, not buff the summoned weapons from ‘Forge Strike’ (the Manifest Armor did get the buff).
The '…and freeze up to 8 nearby normal and magic enemies for 3 seconds" line doesn’t trigger on charge expenditure.
Hopefully this helps sign some light (non-frozen) on the bug(s).