Some of the locked missions are not unlocking after fulfilling the requirement. For example: After winning the battle of Hunters Bane on normal, the Delga Megalift should unlock. Heir apparent, and Coalition Founder has also failed to unlock. V2.6.1 iOS platform
Go to Ship > Captains Log > Awards. Each of the unlocks is visible on this page along with its eligibility in the current game. Very helpful, often showing timeline or difficulty issues that can help you.