Weapon has [?] icon and doesn't register as equipped so i can't use abilities.

Title. My weapon [Sorthalis, Hammer of the Watchers] has a [?] image when dragging into my inventory, doesn't register when equipped. So my paladin cannot use my ability Hammer of the Righteous because it says "Must have a one-handed melee weapon equipped" Despite having it equipped. What's the fix for this.

Are you using a clean version of the game (ie with no mods), on Windows?

Try closing the game, removing the cache folder, then opening the game again.