You open a drawing created in an earlier version of Civil 3D that contains section views with manual drawn objects in them with Civil 3D 2018 and now all your section views have shifted or have been put all on top of each other in one location. (see below)
Civil 3D 2016 Section View
Civil 3D 2018 Same Section View
This is due to Autodesk adding a new setting to the Civil 3D 2018 group plot styles. There is now a check box under the array tab in the group plot style to Add a drafting buffer size to the space between views. (see below)
By default this box is checked so it adding the drafting buffer when you open the drawings in 2018 to the section views. I know at first this is alarming and your wondering how to fix the issue. You can resolve the issue by unchecking the box under the group plot style and the section views should regenerate and go back to where they were originally. (Note: if the section views don't regenerate automatically do a REGENALL and this will force the section views to update)
Civil 3D 2018 with the Add drafting buffer size box unchecked and regenerated section view
You prevent this from happening in the future by Install the Civil 3D 2018.1 update which address this issue so your section views won't shift when first opening the drawing. This update can either be found through using the Autodesk Desktop App or you can download from your Autodesk account page.