Some Windows 10 devices are being automatically opted out of the Windows Insider Program because of a bug in the new Windows 10 Insider Preview Build 18356 (19H1) released yesterday to Insiders in the Fast ring. Windows Insiders who want to check if they’re still enrolled can do so by going to Settings. If the device is opted out, they can opt back in again to get access to the new Insider build. Microsoft is also rolling out a new preview build of the Your Phone app with a beta Phone Screen feature, available in versions 1.0.20701 and above.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10-build-18356-bug-opting-users-out-of-insider-program/