Ue4 "Focus selected" doesn`t work

Anybody know why sometimes focus selected or F key doesn’t respond or doesn’t work. It work only after restarting Ue4. I know there loss information but still maybe someone was facing the problem.

I discovered that the F button will not work when we are using an option “Lock Viewport to Actor”.
To PointLight for example.That was told to do in some tutorial on Youtube.

Hello TazmanGW,

When you lock the viewport to a certain actor you are taking full control over the asset through a first person camera view of that actor. Because you are locked to that actor, you cannot gain focus of another actor in the level.

I hope this makes sense, but if you are still a bit confused or need some more assistance let me know.

Thank you,