Microsoft has resolved a known issue preventing managed devices from receiving the May 2021 Patch Tuesday Windows security updates. The known issue impacted both client and server platforms, from Windows 7 SP1 and Windows Server 2008 SP2 up to the latest versions. Microsoft fixed 55 vulnerabilities, four classified as Critical, 50 as Important, and one as Moderate, as well as three zero-day vulnerabilities publicly disclosed but not exploited in the wild. Microsoft also started rolling out new cumulative updates for all supported Windows versions yesterday.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-fixes-wsus-bug-blocking-may-windows-security-updates/