Sometimes it is necessary to recentre the view on the object or portion you are working on, in orthographic mode press numpad 1 (front view), centre and zoom in to your object or the part of it you are working on, then do the same from the side view numpad 3.
Alternately, the fastest way to do this is to this is to select your object and go to “view-frame-selected” ( numpad . ) this will automatically centre it to the view.
If you are working on a large complex object you can go into edit mode select the verts you want to centre and do “view frame selected” on those verts.
I myself have been plagued the zoom ceasing to function in scenes like the classroom benchmark. If I zoom in too far, it stops working. I haven’t found a solution for this.
I know this is an old thread but I was having the same issue when moving to another Mac. For me I had to change the settings in edit → preferences → “Input”
Select Emulate 3 button mouse (because I am using a track pad)
Then select “OS-Key”.