Windows 10 1903 has an advanced update option that allows you to defer a new feature update for 365 days or a quality update for 30 days. An unacknowledged bug, would cause these settings to disappear on reboot if you change either of them to a non-zero value. Even though the settings would be gone, Windows 10 would still honor the values you previously selected, but no longer provider you an easy way to change them. This was quietly fixed in the optional KB4522355 cumulative update released on October 24th, 2019.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-fixes-windows-10-missing-deferred-update-settings-bug/