Many Microsoft watchers believed that the big Windows 10 Redstone 4 update would roll out to the general public last week. However, the company never publically acknowledged a specific release date, and there have since been issues with Redstone 4 Windows Insider builds that have held back a public release.
In what is being called the latest set of problems, the folks on Reddit have pointed out that there is a currently an issue in the latest Redstone 4 builds where selecting app defaults crashes the UWP Settings app (via Neowin.) Though some Redditors have said they're not experiencing the same issue when going to "Set defaults by app" in the settings, others have reported it as persistent.
— Brandon LeBlanc (@brandonleblanc) April 19, 2018
We're also seeing the same issue on one of our PCs running Redstone 5 build 17643, but Microsoft's Brandon LeBlanc says that it is not in fact "widespread" based on the amount of data available. This may be why another one of our writers running the same Redstone 5 build is not seeing the issue.
Anyway, the problem also appears to be occurring in multiple languages, including Finnish, French, and Italian. LeBlanc also says he thinks the team has "root-caused" the issue and thanked Windows Insiders for offering additional details.
Other comments in the Reddit thread do not make it clear if the problem occurs on upgraded or freshly installed builds, so it will be interesting to see how Microsoft tackles the issue, or if a cumulative update can fix it. There's currently a Feedback Hub thread dedicated to this problem, and it is best to contribute to it if you're also experiencing the same issue with the Settings app.