Apparently designer.exe hangs if the new webengine dlls are present. The dlls can be removed, but then, what if you need them? The easiest way around this problem for me was to use the mingw Qt 5.7 binaries for designer.exe (without including webengine) and leave the vs2013 binaries alone. I’m sure Qt will be fixed soon, but this will get you rolling in the mean time. Happy Coding!