This article applies to K2 upgrades on Windows Server 2012 R2 that has had the Microsoft July 2018 security update applied. The fix is manual and not available in the Microsoft Update Catalog until approximately September 2018.
The K2 Setup Manager hangs when upgrading K2 on a Windows Server 2012 R2 that has the July 2018 Security Update applied to it.
The Microsoft July 2018 Security Update has a known issue that the W3SVC remains in a "stopping" state, but cannot fully stop or it cannot be restarted. Due to this, iisreset command occasionally does not work causing HTTPS calls to hang indefinitely.
Microsoft has a fix available: Improvements and fixes - Windows 8.1 and Server 2012 R2. Currently you must install the fix manually as it is not available in the Microsoft Update Catalog until September 2018.
Use this PowerShell script to install the update, restart the server, then restart the K2 upgrade: