support.microsoft[.]com/en-us/help/4577063/windows-10-update-kb4577063
There are a lot of fixes in this one -- it actually might have fixed a problem I was having -- but they'll also be in the regular October update, though Microsoft will probably not list them... don't know why, but Microsoft publishes a much fuller list for the update preview than for the regular update that follows.
And since resuming the 2nd monthly Win10 update, Microsoft still hasn't gotten the installation right. The Windows Update page in Settings shows a link for optional updates. Click that, and then click the drop-down, and you can click to check the box for this update preview. Click Download and install, and you're back to the Windows Update page in settings, where Win10 checks for updates, then tells you there aren't any. Open Task Mgr. and you'll find that's just plain wrong -- you'll see Windows Update working. When you don't see it working any longer, that *probably* means it's done, and if you open the Windows Update page in Settings, if it is done, you see a Restart button -- the notification you get with regular updates when it's time to restart doesn't happen. Finally, to add a bit of insult, checking the Windows Update in Settings after that restart, it's shown me that another update preview, this time for .NET, has completed & needs a restart.
Been testing a few days after installing this update, and so far nothing bad to report.