This is not showing up for me. I've manually check for updates several times. Only see 1.5.5 - iOS 12.1, iPhone XS (but then 1.5.6 never showed up). Also checked on friends iPhone 6 and another iPhone 7.
The new update is slated to launch today and is released in phases. If you don't receive the update by tomorrow, please let us know and we'll investigate the issue further.
