It means the process doesn't always work and the miles are not always automatically reinstated. Confirm the miles are reinstated when cancelling award travel. In the event the miles are not reinstated, call to have customer service process the reinstatement.

The reinstatement isn't always obvious due to the "dashboard". I generally note the total at the time of cancellation and determine the number of miles to be reinstated. The total doesn't update immediate but the "Activity" portion of the dashboard does update immediately. Finding the reinstatement in the list of activity may be problematic, though. Generally I wait a few hours and check the total to determine if the miles were reinstated. As noted, the reinstatement issues are with partner awards.