I’ve been copying and pasting some Detail windows from one file to another, and it seems to import the clipping settings for the original file, but without a Clipping plane, resulting in a Detail that is clipped and cannot be unclipped. I have selected every Clipping plane and disabled it in the Detail, and there are no hidden/locked objects and all of the layers are on.
Attached is my system info. I have also attached 2 files as an example of what I am talking about. File 1 is a simple box with a clipping plane, and three views on a page layout. In File 2 I created a sphere in a new document, and when setting up the page layout, I copy/pasted the details from File 1. You should see that File 2 now has a clipped viewport, despite there being no clipping plane in the file.