Windows 10 registry hack appears to be the only 100% fix for this issue and it also disconnects Bing and Cortana online services from Windows 10 search. As detailed on Reddit, you need to perform the following steps: 

• Run Regedit.exe
• Navigate to HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Search
• Look for ‘BingSearchEnabled’, if you don’t see it you will need to create it (right-click in a blank area, pick ‘New DWORD’ 32 bit. Type in ‘BingSearchEnabled’
• Open BingSearchEnabled, set it to 0, press OK.
• Look for ‘CortanaConsent’, again create it if you don’t have it using the method above. Also set it to 0.
• Reboot.