3445413 - SAP GUI for HTML is not loaded with many 404 errors in F12 developer Tool

• WebGUI (SAP GUI for HTML) is showing "Please wait" when calling from FLP(Fiori Launchpad)
• WebGUI shows error:
  Message Bar
  x
  Stop Application
  x
  EmphasizedPrevious...
• WebGUI is not loaded after logon (even bypassing FLP)
• Open F12 developer tool to check the traffic trace, there are many ERR_ABORTED or 404 Not Found error within files under icmandir, below shows some of the example error log:
  

  https://hostname:port/sap/public/icmandir/its/lsgui/js/its_utils.js?xxx
  net::ERR_ABORTED 404 (Not found) 

  https://hostname:port/sap/public/icmandir/its/lsgui/js/its_frameset.js?xxx
  net::ERR_ABORTED 404 (Not found) 
  ...

  https://hostname:port/sap/public/icmandir/its/ls/theming/UR/ls/sap_corbu/standards.css
  caught ReferenceError: owguDOM is not defined
      at Frame.create..
  

Notice in this case WebGUI alone doesn't work. The error message might be different when calling WebGUI alone than when it's called from FLP.
If webgui alone works, then it's not covered in this KBA. 

WebGUI

ERR_ABORTED, 404, Not found, webgui, flp, please wait, blank, not loaded, its_utils.js, standards.css, its_frameset.js, owguDOM is not defined  , KBA , BC-FES-WGU , SAP GUI for HTML , BC-CST-IC , Internet Communication Manager , BC-FES-ITS , SAP Internet Transaction Server , Problem