Extra Credit Achievement Bug 89/90

Hi, I am having a problem getting this achievement on the Xbox One, I currently have 89/90 Mission Specific Assault Ops Complete. The sidearm slaughter for me is 1089/50 which seems to be glitched and was not counted for completion. Please help me as soon as possible, Thanks.

Also, I am running off of the Games with gold for Spartan Assault.

I see you found the best place to post about this. I’m just replying to link others to the best place.

Thanks for the help, MathGuy42.

To ChancePW, as you have already found the appropriate thread to discuss this issue and utilize the workarounds, I will be locking this thread.