Chain Command Blocks Not Equipping Armor?

The following command is used to force the player to equip armor:

/replaceitem entity @p[type=Player] slot.armor.head chainmail_helmet 1 0 {display:{Name:"Archer Helmet",Lore:["You feel somewhat faster, and resistant to ranged damage"]},AttributeModifiers:[{AttributeName:"generic.movementSpeed",Name:"generic.movementSpeed",Amount:0.10,Operation:0,UUIDMost:24682,UUIDLeast:195471},,{AttributeName:"generic.armor",Name:"armor",Slot:"head",Amount:2.0,Operation:0,UUIDMost:100,UUIDLeast:100}],ench:[{id:0,lvl:2},{id:4,lvl:2}],Unbreakable:1}

And when run in a command block, it works 100% fine, but when it is part of the chain, it gives the output saying:

[14:09:34] Replaced slot slot.armor.head with 1 * [Archer Helmet]

However no changes were made to the player’s GUI. Any ideas why this would happen? I’m playing Minecraft 1.10