Not sure what it is but added to an existing save and tried to build but my pawns will not build the pews. They will deliver the resources and I cannot force them to build them, its only with these pews and no other item.

Which specific seat is this? And can you send me your modlist? I'll have to update the desc that it may not be safe to add to existing saves.

Edit: Unsure if this is what you're experiencing, but have just fixed a bug with building cushioned pews from pews (and drum benches from stools)