https://www.techradar.com/news/microsoft-reveals-why-spring-creators-update-has-been-delayed

We were disappointed when Microsoft delayed the Spring Creators Update, its next big overhaul of the Windows 10 operating system, but also curious to know what was serious enough to halt the much-hyped update, and now Microsoft has revealed why.

In a blog post announcing the release of Windows 10 Insider Preview Build 17134, Dona Sarkar, who works at Microsoft, revealed that as “Build 17133 progressed through the rings, we discovered some reliability issues we wanted to fix. In certain cases, these reliability issues could have led to a higher percentage of (BSOD) on PCs for example.”