As mentioned in the title, the CWL mods Powerful Friends and Radiant Light are meant to provide a significant stat boost if another arc mod is slotted into the same piece of armour. The new Arc Siphon mod does not trigger the bonus stats, even though it is shown to be an Arc mod. All other arc mods I've tested seem to work fine, I'd guess the issue is related to Arc Siphon being a recent addition to the game.