Just upgraded to Windows 1903 and hit this myself, seems Microsoft decided to assign the raccourci clavier for the new Office App to Win+Ctrl+Alt+Shift! (aka HYPR key combination for QMK users)
Changing the open command for this raccourci clavier to rundll32 resolved the issue for me. Using an elevated cmd, run la commande suivante:
REG ADD HKCU\Software\Classes\ms-officeapp\Shell\Open\Command /t REG_SZ /d rundll32