How do you edit the fields displayed on the mini page layout within Lightning? I've set it in Classic and it displays correctly, but in Lightning, when I hover, the popup only shows the record name.
In lightning the mini page layout looks like it is controlled by the compact layout on hover and not the actual mini page layout .
Every object will have a compact layout ,clone and make a new compact layout and add necessary fields and you will see the lightning experience hovers reflect the compact layouts
The hover details