When opening an EMB file, it takes around 10 seconds to get design preview showing up in the Open dialog box. As the consequence, Open dialog box is hanging for around 10 seconds to get EMB file opened.
Turn off "Details pane" in the Open dialog box. The issue is caused by "Details pane" in the Open dialog box. It seems Windows OS system is collecting the design information from EMB file to display in "Details pane", it takes time for such procedure. It is unnecessary to have design information displayed in "Details pane", as such information is displayed in the Preview box of Open dialog box already.