As title suggested. In a clean install Win10 RS1 14393.10 x64 enterprise, sometimes after you click a UAC prompt to allow a program to install (for example Google Chrome), it will either just sit in there doing nothing, or progress at 0% forever. This stupid bug was repeatable in all my computers, with vastly different configs. Long gone are the days of Windows 2000 and XP days. The OS was simple, direct, and do stuff you told it to do. Nowadays, stupid Windows 10 owns you and your computer, and poops on you when you ask it to do something.
I totally agree with you. In the half dozen clean installs I've done I've seen a number of "odd" things that I haven't experienced with the older builds. I can see today I've got a 4GB+ $WINDOWS.~BT folder on my workstation. I know what's coming... Haven't seen your issue though...
I know UAC has had that bug for a couple months now where if you have it set to "not dim" and run programs directly from Explorer, sometimes UAC will hide itself behind Explorer, forcing you to surface it via Alt-TAB or by clicking the taskbar. I just put it back on dim for now.