AutoCAD / Civil 3D
Objects get cut off when zooming in perspective view
https://forums.autodesk.com/t5/autocad-forum/objects-get-cut-off-when-zooming-in/m-p/9170687#M1001566
it's perspective mode, a display clip is needed as the camera (you have virtually) can't look behind your location.
You can play with system variable PERSPECTIVECLIP and change it from 5 to 1, run _REGEN .
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