List item opening in right 'preview' pane instead of new page/selected column item missing

LeslieBrado , your List works fine, is it is now a modern List instead of your accustomed classic SharePoint 2013 List. You have at least 3 options now: 

1) this option is not a good one, because you can use the old layout, but you won´t learn the new way of working with it: to switch back - if your admin admits it - you can go to your List, then click on the Gear Icon in the upper right, then go to list settings. In that page you can click on the link "advanced settings" and then scroll down on the very bottom of this page. There is a check box for this list to turn back to the classic layout instead of the new modern layout. Then click OK. I don´t know if you ll see then the new item form, but at least you ll have the menu bar instead of the modern edit panel on the right.

2) next option is the better one: Learn to explore the edit panel in the modern list you have now. I really like the new way of the view settings, the filter possibilities and the info icon. This info icon is mainly this, what you had so far in the classic form of your list items. BUT: it is far more easy to deal with and the responsive usability on every device is phenomenal I think. For a quick intro I recommend this intro to you: https://www.youtube.com/watch?v=HKywJ6w-rjA

3) The queen of all SharePoint Forms is not SharePoint alone from now on - it is the possibility the adjust your List Items Form with a PowerApps Form, if you are at least a Site Owner with the permission to build and create your own low-code form on a modern SharePoint List. https://www.youtube.com/watch?v=58d4hZmqltM 

So I hope that helps you a bit to get a slight orientation on how to deal with the new ways in List Forms of your modern SharePoint. Or with your classic SharePoint, waiting to expand your better options with your SharePoint Lists and learning your new routines! Happy SharePointing, give a Like, if it helps. Greets, Eva.