Halo: Spartan assault

Hello, I have a problem of success on the game Halo: Spartan assault on Xbox one. on Success “Additional Credits: Complete All Assault Operations Specific to the Campaign Mission” I explain to you my situation of the problem of the challenges specific to the mission. the first challenge of the mission operation A is “you shoot or you point: kill 3 grognads minors with fragmentation grenades” and I’m 221/3 and for the second challenge of Operation A mission, it’s “beginners’ bullets: kill 20 minor elites” and I’m at 445/20 I do not know what to do to get success, can you help me solve this problem?

The “Extra credit” achievement may be glitched. A workaround to this is to complete one of the weekly challenges; follow the steps in this video, there’s a good chance you’ll unlock it.

Are these achievements still attainable with a Windows phone?

Xbox one