Guild Wars 2

The right-mouse button is used both for moving the camera and for selecting targets. Normally, it should do either one or the other, but frequently it does both at the same time. This results in constantly losing targets in the middle of fights, to the point where spells just don’t hit anything because the target was lost midcast.

Possible solution would be to remove right-click selecting or to make it optional.

That is already in your options. Take a look and disable right-click to interact or attack.
I also enable Double-click To Interact so a double left click interacts with NPCs.