Microsoft aimed to start the rollout of Windows 10 Creators Update (aka build 1803) on April 10 but the big launch got foiled at the last moment. Windows Central heard from its sources that over the weekend, Microsoft developers discovered a major bug in the update. The problem isn't exactly clear, it's said to be a rare bug that can cause a high impact. The site claims this means the launch may be delayed by several weeks.
Microsoft has decided to hold the release of Version 1803 until the company can verify the bug has been resolved, which means it'll likely be another couple of weeks before Version 1803 is given the green light for rollout. Luckily, there's no real rush for Microsoft to get this release out the door, so it can (and definitely should) take its time with this. I believe build 17133 is still the RTM, for those wondering.