Yesterday you should have seen Microsoft actually release the Spring update for Windows 10, as it seems now the launch was canceled as Microsoft spotted a rather nasty bug.
Microsoft watcher Zac Bowden reports that the bug in the Spring Creators Update (version 1803 of Windows 10) was spotted by participants of the Windows Insider program.
Got some more info on this: Microsoft was going to rollout on April 10, but found a blocking bug over the weekend that was bad enough to hold the release. Not sure if bug was fixed in 17133.73 or if it'll come in another patch. RS4 will likely begin rollout in a couple weeks now.
Little is know about the bug aside that it is called a 'blocking bug', but for Microsoft to stop such a big update, well that's quite something. Word is that it would only affect a small number of users, but would have a large impact. Once Microsoft verified the problem has been fixed, Windows 10 version 1803 will be released somewhere this month.