Hiya
Okay, it may not be super obvious when looking at the modifiers, but everything is counted correctly here.
On the third line you see:
Shield (+3 Frostward), bonus +5Then, two lines below, you see:
Left hand item (+3 Frostward), bonus +1So you're getting a +6 bonus to Armour Class from holding this artifact light shield.
The +5 bonus includes +1 from the fact that it's a light shield, +1 from your feat Shield Expertise, and +3 from the shield's magic enhancement value.
The final +1 is a special bonus from this artifact item. In the item's description, you'll see the last line << Give bonus Armour Class, Generic, +1 >>.
Cheers
