Some users of Windows 10 Build 10130 for PCs were having issues of unresponsive flyouts from taskbar including Start. Actually when this build 10130 was released, Microsoft had listed this issue under known issues:
In some cases, flyouts from the Taskbar (including Start, Cortana, Network, Battery, and Action Center) fail to fly out. This is a transient issue, and after retrying a few times it will succeed. We are also working to service this issue with an update.
And Microsoft had mentioned that its working on a fix. And today users of Build 10130 received an update to fix this issue via Windows Update.
The KB3070365 is the fix received via WU:
Symptoms: When you click icons on the taskbar (including Start, Cortana, Network, Battery, and Action Center) in Build 10130 of Windows 10 Insider Preview, the expected flyout might not open.
This update is available from Windows Update. You must restart the computer after you apply this update.