A new cumulative update is rolling out to Insiders that are on the Release Preview ring, which is build 14393.726 for both PC and Mobile. The new update comes exactly two weeks after the last one that reached the Production ring, 14393.693.
As you should be able to guess by now, there is no changelog available just yet. It's unclear why the company seems to have so much trouble with publishing release notes at the same time that an update is released, but if Microsoft does publish them, they'll probably show up in the Feedback Hub.
Also, it's worth noting that if Microsoft doesn't offer a changelog at all, it certainly wouldn't be the first time, so you probably shouldn't hold your breath for this one. We've reached out to the company for comment.
First spotted by Windows Central, the update will show itself as KB3216755 on PCs. If you're already on the Release Preview ring, you can grab it on your device by checking for updates. If not, you can always go to the Windows Insider Program tab and click "Get started".