This guy have a similar problem:
I tried unchecking the lock to cursor but it STILL doesn’t appear, it ONLY appear from the camera’s perspective, this indirectly means there is no way to manipulate the camera using the gizmo !
Incase of Fanboy reply: “You don’t need it anyways ! Just press G and then ~”
Yes, I know this, I want the gizmo, is this a bug ?
Can you provide more information about your computer? Most importantly, what operating system and what video card do you have?
Hello fweeb.
The very fact that it works inside camera’s view already means that it is not a video card issue but I can understand why you might ask that as you are trying to help, thank you anyway 
Still worth an answer to rule out low-hanging fruit.