Microsoft found issues with the Spring Creators update RTM Build 17133 and has decided to push a new Build 17134 with fixes to address these issues. So, this means Build 17133 is not anymore the RTM Build losing that status to this new build.
Today, we are releasing Windows 10 Insider Preview Build 17134 (RS4) to Windows Insiders in the Fast ring. This build has no new features and includes the fixes from KB4100375 as well as some fixes for general reliability of the OS. 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. Instead of creating a Cumulative Update package to service these issues, we decided to create a new build with the fixes included. This just reinforces that Windows Insiders are critical to helping us find and fix issues before releasing feature updates to all our customers so thank you!
So, it seems Build 17133 was causing a higher percentage of BSOD and could have been a disaster in making for Microsoft.