My achievements don’t activate for around 12 hours

Hi there Shane! My name is Gerardo and I'm an Xbox player like you.

This issue can sometimes occur if you complete achievement tasks while your console is offline.

First of all, ensure that your console is connected to the Xbox network by going to:

Profile & system > Settings > General > Network settings.

You can select "Test network connection" to diagnose your network connection.

If your Xbox network connection appears to be working fine, try the following steps to see if they resolve the issue:

1. In your console settings, go to the "Account" section and select "Remove accounts." Choose your account. This will remove your profile from the console, but you won't lose any data.

2. With the Xbox on, press the power button on the front of the console for 10 seconds until it turns off completely. Keep your finger on the button even if the light goes out before the full 10 seconds have passed.

3. Unplug the power cord from the console and wait for 30 seconds.

4. Reconnect the power cable to your console and turn it on normally.

5. Add your account back to the console so that all your profile information is downloaded again. This process also helps to synchronize the licenses of your account on the console.

6. Check if the problem persists.

Please let me know if you have further questions or If the issue continues.

Diablo challenge is sitting at 100% and not unlocking. Same with around 8 other achievements. The challenge is concerning due to it only having about 12 more hours Untill it expires.

Hey I'm having the same problem, no response to my post yet either, but I found this article on their support site, check it out if you haven't already. It didn't solve any of my problems but there's a survey on the page that they say they will forward to
the proper support team, has only been a few days but hoping for a response Good luck! I got all of the achievements throughout the legendary campaigns until Halo 4. Didn't give me Requiem or the Halo 4 game ending or MCC completion achievements!! Was waiting
for it and nothing ever popped , hopefully these guys get back to you as well:

support-origin.xbox.com/.../troubleshoot-achievements-challenges

Also, in an old thread i found some folks actually got help with this, the support crew needed the info you give in the survey (date and time and name of achievements you missed)

Here's mine:

Requiem (sometime between 12/20/15-12/23/15, probably closer to 12/22-23)

Herald of Reclamation (12/24/15 around 1am)

Veteran (12/24/15 around 1am)

War Hero (12/24/15 around 1am)

Legend (12/24/15 around 1am)

Wake Up John (12/24/15 around 1am)

I Need a Hero (12/24/15 around 1am)

The Legend of 117 (12/24/15 around 1am)

Lone Wolf Legend (12/24/15 around 1am)

Also "Librarian's Gift" (12/24/15 around 1am)

Maybe one of our threads will get a response

forums.xbox.com/.../2095450.aspx

My achievements are not working either. I noticed this 12 hours ago and may have been going on for the last 24 hours.

I hope Microsoft is aware of this.

Achievements don’t unlock instantly when you complete them

In some instances, you may meet the requirements to unlock an achievement but not immediately receive a notice or update to your gamerscore. The Xbox Live service validates the unlocking of achievements and, though rare, delays can occur. Don’t worry – your
progress has been recorded and the achievement will be awarded shortly, usually in less than 24 hours.

Achievements and challenges not unlocking while offline

For achievements and challenges to get unlocked and for rewards to be issued, you must have an active connection to Xbox Live. Though you may be able to meet the requirements for an achievement or challenge while offline, you will not receive related notices
or rewards until you connect to Xbox Live.

A challenge disappeared before you could finish it

Challenges are time-limited, sometimes to weeks or months, sometimes to just hours. If you don’t complete a challenge within the time window it’s available, you will not receive a reward.

No gamerscore earned from app achievements

You can earn app achievements for basic use of an app (such as, watching a movie on Netflix), at the app developer’s discretion. App achievements do not affect gamerscore, though they may bring other in-app rewards.