I switch a lot between the Piano Roll View and Track view and I use a lot the editing tools.
I do not understand why sometimes, for no apparent reason, F5 to F10 stop responding and I have to use the middle mouse button to access these tools again, or I have to restart Sonar.
Does anyone have any tips?

You may have a key next to the Insert key on your keyboard labelled Function. If you've accidentally pressed it, it will disable the Function keys.

mudgel
You may have a key next to the Insert key on your keyboard labelled Function. If you've accidentally pressed it, it will disable the Function keys.

 
It's not my case.
This is certainly a bug in X3e.
But I still can not figure out what action I take for this to happen.
I will try to observe more.