I obtained the Underlight Angler yesterday, and after obtaining the 100 AP needed to activate it, the Soul Forge for my class (Death Knight) does not activate while I have the weapon equipped or unequipped – nor does it take effect regardless of whether I am with/without my Legion artifact weapon.
There’s a separate post regarding a problem with an Underlight Angler that’s already began progression on its traits. From that post, it seems like there’s a problem with this fishing pole since end of Legion. Blizzard seems to have left this issue on the sidelines for an entire expansion…