Another bug in the upcoming Redstone 4 update for Windows 10 could potenitally add another delay to its roll out, depending on how things shake out. Over on Reddit, several users have noted a weird issue that is causing the Windows 10 Settings section to crash when selecting the "Set defaults by app" setting. If you have one of the preview builds installed, you can see if you are affected by heading to Settings > Apps > Default apps > Set defaults by app, and then selecting the related option.
It does not appear that everyone has this issue, though there is enough chatter that Microsoft decide to hold off pushing out a finalized build, outside of its Windows Insider program where new releases are tested. What makes the situation a bit difficult to analyze is that nothing is official—Microsoft has not yet announced a release date, or even confirmed what it will call Redstone 4.
There have been references to this update being called the Spring Creators Update (the previous one was called the Fall Creators Update, and prior to that Microsoft rolled out the Creators Update). More recently, however, reports emerged that Microsoft would be calling it the April 2018 Update. If that is the case, then Microsoft would need to make a strong push to fix whatever is wrong with Redstone 4 and deliver it this month.
While never announced or confirmed, the latest major update to Windows 10 was expected to release on April 10. That day came and went, however, with reports of a last-minute bug discovery. Not long after, Microsoft released a new Redstone 4 build to Windows Insiders.
"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," Microsoft said at the time.
It's a bit unusual for Microsoft to release a second RTM (Release To Manufacturing) build, and depending on it wants to handle this latest bug, there could even be a third. This bug actually dates back to build 17634, though is still garnering attention and apparently causing problems.