Using C_ContentTracking.StartTracking on completed achievements sets them to be tracked, but they are not shown in the objective tracker. With the limit of 10 tracked achievements at the same time, it is possible to soft-lock the objective tracker. As tracked achievements are also stored between sessions, this problem persists (if caused by an addon) even after removing the addon. The only way to remove tracked completed achievements is with C_ContentTracking.StopTracking.
Using
C_ContentTracking.StartTrackingon completed achievements sets them to be tracked, but they are not shown in the objective tracker. With the limit of 10 tracked achievements at the same time, it is possible to soft-lock the objective tracker. As tracked achievements are also stored between sessions, this problem persists (if caused by an addon) even after removing the addon. The only way to remove tracked completed achievements is withC_ContentTracking.StopTracking.Edit: Currently only tested on retail!