Microsoft released a surprise update that upgrades Windows to build 18362.30 (KB4497464) to Windows Insider in the Fast and Slow rings in order to resolve a few issues. Microsoft announced today that build 1903 is officially called the May 2019 Update. This update will be released to Windows Insiders to test starting next week, but before that they first need to fix a few bugs in the build. The most problematic issue is one that could cause Windows PCs to become unbootable after installing a cumulative update followed by a optional feature-on-demand update.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10-insider-build-1836230-released-to-fix-boot-breaking-bug/