It seems that Activision has recently made a back-end change that sets all Call of Duty accounts to private, by default.
https://twitter.com/status/1349891676547002370

Because of this, we cannot track your accounts unless you set your profile to public. However, we understand the reason for the change and fully respect Activision's decision.
Thus, we decided that instead of using workarounds, we will disable, temporarily, the Call of Duty tracker. Your stats and matches will still be kept, for now.

We have already started working on a new API which will allow you to authenticate with Activision and pull your data, regardless of your privacy.

Stay tuned for more info..