The Android 5.1 update from AT&T meant for the 2013 Moto X has been suspended for unknown reasons. AT&T has posted this on treir software update page, saying that it has paused the push, as they are trying to solve this issues.
Here is the official word from AT&T:
"Effective July 20, 2015, the Android 5.1 (Lollipop) software update for the Moto X (XT1058) has been temporarily suspended. We apologize for any inconvenience and are working to resolve this issue as quickly as possible."
While AT&T has not provided a valid reason for the pull, there are a numerous discussions going in the Android Central forums about numerous bugs that have surfaced following the update, including an increase in static noise from the speaker, where as others are unable to adjust APN settings.
Hopefully AT&T will be able to push out another update as soon as possible. If you have experienced such types of issues after the update from AT&T, be sure to join the discussion.
You can discuss here