Dragons Teeth: Bulletproof. Sort Of.. achievement broken, Xbox One

FINALLY UNLOCKED!!! Well... This was really weird, and I must say that I think now it was all Microsoft's fault. I've tried all recommendations (play more matches, reuse the shield, delete/redownload profile, delete/reinstall the full game, reset Xbox to factory settings). Nothing. I've unlocked one of my last missing achievements (Risky Business) on Saturday August 2nd to push, and nothing. But here comes the weird thing:
I stop using my console on August 3rd. Went on vacations, disconnected all power supply at home, returned today (August 11th) and doing movements in my Live account in the PC (nothing special, only verifying my membership expiration date), I realized that in the "last activity" section the "Bulletproof. Sort of..." achievement appeared as unlocked... When? On August 2nd. Why on that date? I've completed since July 24th. Without turning ON the console. I connected my One, started up, expecting to see the achievement popping, but nothing. No pop, but the achievement is there, completed and unlocked.

Thanks to all for trying to help. This is a case for the Twilight Zone...