The Cozy Tiger Pajama Hat appearing as "locked" is not a bug -- this item is intentionally locked at first and can be unlocked by reaching Friendship Level 5 with your new companion, Rajah. You can find this information in the item's description by selecting the ⓘ Information icon, which will display the unlock requirements. Once you reach Friendship Level 5 with Rajah, the hat will automatically become available in your Inventory!