Hey,
New versions aren't immediately made available for auto-update. Releases are given a week or more to verify their stability. Then, if all seems to go well, they are make available on the auto-update API. It just so happens that an issue was found in 12.5.3.0, so it wasn't put on the API. 12.5.4.0 has been made available a few days ago, and should in all likelihood be made available on the API within the next few weeks.