For all preview build I have installed to date (on 20298 at the moment) I have pop ups that keep appearing. I will get one that says "We are adding new features to Windows."..... then another after that says "Something happened and we could not install a feature." I have no idea what it is trying to install so no way to diagnose the issue.
Also I have it promoted to domain controller, in this mode it seems that the night light cannot be enabled.
I also find that the screen saver /display turn off will not always function, even when nothing should be stopping it. If I use powercfg -requests in CMD then it shows nothing is stopping the display from turning off. I have turn off display after 1min, blank screen saver after 1 min with require logon to resume. Works most of the time then may not work for other times. Strange.