Xbox Tenure years recently disappeared after the recent update Delta preview of the update.

Seems you have to be invited to join the Alpha ring

https://support.xbox.com/en-US/xbox-one/console/xbox-insider-program

The current Xbox One Update Preview rings are:

• Alpha – Open on an “invite only” basis and receives updates at the earliest point in the preview window.
• Beta – Open to Xbox Insiders with a Program tenure of 3 or more months and an Xbox Insider XP Level of 5 or higher. This ring receives updates shortly after Alpha.
• Delta – Open to any Xbox Insider with a tenure of 1 or more months that has reached Xbox Insider Level 2 or higher. Depending on certain edge cases where further attention is required from Alpha or Beta rings, Delta Insiders may receive
  system updates before Beta, though this is not a common scenario. Additionally, while early system updates are not guaranteed across the Delta ring, all Delta Insiders will receive the update prior to GA.
• Omega – Open to anyone and receives system updates shortly before the GA (General Availability) release.

Did you recently change to 15 years tenure? This happens to me every year when I go up a year in tenure. It disappears for a few weeks then suddenly it reappears.

I really wouldn't like to say yes to that as the Omega ring gets updates just before general release so the odds aren't good.

The current Xbox One Update Preview rings are:

• Alpha – Open on an “invite only” basis and receives updates at the earliest point in the preview window.
• Beta – Open to Xbox Insiders with a Program tenure of 3 or more months and an Xbox Insider XP Level of 5 or higher. This ring receives updates shortly after Alpha.
• Delta – Open to any Xbox Insider with a tenure of 1 or more months that has reached Xbox Insider Level 2 or higher. Depending on certain edge cases where further attention is required from Alpha or Beta rings, Delta Insiders may receive
  system updates before Beta, though this is not a common scenario. Additionally, while early system updates are not guaranteed across the Delta ring, all Delta Insiders will receive the update prior to GA.
• Omega – Open to anyone and receives system updates shortly before the GA (General Availability) release.

https://support.xbox.com/en-US/xbox-one/console/xbox-insider-program

Hey there!

If you recently renewed your Xbox Live subscription your tenure may take a bit of time to update on the Xbox One, be sure to keep an eye out for the change as it may take a bit of time. Thanks for your patience on this!

No. I've never lapsed and my tenure is reporting inaccurately by 3 years. If you search tenure in the forums, you will see thread after thread regarding tenure reporting inaccurately for years now. Tenure reporting is obviously broken.

You just have to continue to be active in the program, take part in surveys, etc. but Alpha is also by invite only so you would have to wait to be invited into it by Microsoft.

How do the Xbox One Update Preview rings differ and how do I change rings?

There are four Xbox One Update Preview rings, which allow you control when and how often you will get early access to console updates. You’ll gain access to rings based on your activity as an Xbox Insider. If you’ve been invited to more than one ring, you
can switch between them from the Xbox Insider Hub.

The current Xbox One Update Preview rings are:

• Alpha – Open on an “invite only” basis and receives updates at the earliest point in the preview window.
• Beta – Open to Xbox Insiders with a Program tenure of 3 or more months and an Xbox Insider XP Level of 5 or higher. This ring receives updates shortly after Alpha.
• Delta – Open to any Xbox Insider with a tenure of 1 or more months that has reached Xbox Insider Level 2 or higher. Depending on certain edge cases where further attention is required from Alpha or Beta rings, Delta Insiders may receive
  system updates before Beta, though this is not a common scenario. Additionally, while early system updates are not guaranteed across the Delta ring, all Delta Insiders will receive the update prior to GA.
• Omega – Open to anyone and receives system updates shortly before the GA (General Availability) release.