Does Shield stack in Frosthaven?
Yes. Shield from items and abilities add together, and the total reduces each attack against you. It does nothing against damage that is not an attack.
Shield is one of the few bonuses that always adds up. A character with Shield 1 from an ability and Shield 1 from an item has Shield 2 against every attack that round.
The total is applied as a single reduction to the attack value, so the order you added the sources never matters.
What Shield does not do is stop everything. Retaliate damage, traps, Wound and Bane are not attacks, so Shield does not reduce them.
“Multiple shield bonuses stack with one another as a single reduction in attack value. A shield bonus does not apply to sources of damage that are not attacks.”
Rules change with errata and with digital patches. If your copy of the book disagrees, the book wins — the official Frosthaven FAQ is the next place to look.