@dipesh, thanks for your suggestion.
I checked the registry entry of my two computers, both of which have same problem.
The screenshot of regedit is attached. As you can see, there are 21 entries of icons in this registry entry. It is over the limit of Windows (15) and maybe this is a cause of problem.
I use OneDrive, Insync and Dropbox and none of them cannot be uninstalled. So, I should be patient until Microsoft changes this limitation …
