Hey,
I´m not sure whether I understand you correctly but am I right that the issue you´re having is that when you zoom in, the object you had your mouse on shifts to the middle of the screen? Because you´re zooming onto it? If not how does your desired zoom differs from what you have right now?
If the object is actually moving away from the mouse: How do you perform your zoom? Could you post the code/blueprint here?
Intuitively I would say right now that it should work if you move the camera towards the location under your mouse without rotating the camera at all.
This way the object should stay at it´s relative position on your screen and just grow in size while you get closer but not move away.
You could archieve this by linetracing under your mouse or getting the hit result as you said and then taking than location and subtracting your camera position from it.
That will give you a vector pointing straight from the camera to the location.
You could then interpolate the camera position along that line by adding fractions of that vector to your camera position while you zoom which should hopefully zoom you onto the object the way you wish.