Shutter help

Ok, I am now running into a confusing issue and I am not sure what is going on.

I am running my D3400 Nikon.

I have found that as I am playing with the aperature and learning how they all work together.

When I go to snap a picture, say of my family with a background, the camera will not click the shutter. Instead, it gives me an R number in the viewfinder and just sits there. I go to lower the camera to see what is going on and it snaps a picture of the ground!

I go to try and snap another picture and it does the same thing. However, I zoom in a little, and it clicks a picture!

I have tried the aperature, I have adjusted the ISO, I have played, even, with the Shutter speed, and nothing.

But this does not happen all the time. It happens once in a while, and sometimes at the most inopportune time (when extended family want a family picture and it doesn't take.

I have changed the lighting sensitivity as well, used the guide function, and then the manual. Nothing.

Any help would be appreciated. Thanks in advance.