I have never seen this error message before. The popup in the lower right of the attached image is what I saw when I started Civil 3d just now. Clicking it brought up the dialog box, which I have also never seen. As there are clearly hatch patterns in the drawing behind, WTF is happening here?
I have Civil 3d 2018.3, Autocad 2018.1.2, and Map 3d 2018.0.1 installed.
My guess is that the detail was created using a custom hatch pattern. And you don't have the path set in the support path settings to read the custom .pat file.
Good thought, but I don't see anything that has changed regarding my paths. Besides, if Autocad can't find a hatch pattern, it gives a completely different error message, then proceeds to use whatever pattern is available (usually solid). All of the hatches in use in this simple detail drawing are displayed correctly.
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