Sometimes I find difficult to reboot either from the widget and from the application launcher.
If I click on "reboot" nothing happen. The only way to do that is through terminal.
Once i reboot the system everything (application launcher and the widget) works fine. Is that some sort of bug?

There is a well known bug relating to something that happens when kde/plasma libraries and/or apps are updated causing in library reference discrepancies which result in degraded funtionality, which is why it's a good idea to reboot after running updates (whenever it suggests a reboot is needed)

Thank you very much for your answer.

I have a similar problem with my little son laptop. It runs KDE neon as well and everytime he let his laptop "suspend" the session he won't be able to reactivate the desktop. The only option he has is to mechanically switch off the laptop and switch it on again as the computer won't recognize any input from mouse or keyboard. Is it still related to the same bug?