Why is Windows 10 Search not working?

[Windows Central Question]

After upgrading to Windows 10, it used to work without any problems. But after 3 days the result doesn't load. After typing the word all I see is the loading dots. I have tried refreshing the index, troubleshooting etc etc but it doesn't fix this problem. Sometimes if I leave the loading screen for 15 to 20 minutes the results are shown, but why does it take so long and why it doesn't show the results the rest of the time?