You may notice some visual differences when you open a drawing in the AutoCAD web app. None of the data in your file has been modified. However, some external references, 3d geometry, "proxy" objects, and some other object types may not display. Also, font types will look different. If you open your drawing in any AutoCAD desktop product (AutoCAD, AutoCAD LT, DWG TrueView, or an AutoCAD vertical product), you'll still see an accurate representation of your file.
Certain font styles will not display and have been substituted with Simplex.shx.
Certain object types will not display. Once again, these objects have not been removed from the drawing, but are only visually absent. This includes proxy objects and custom objects, including objects from AutoCAD Mechanical, Electrical, Civil 3D, Map 3D, MEP, P&ID, and Plant 3D.
Point clouds, underlays (such as PDF or DGN underlays), and certain images and other types of external references will not display.
The following image types can display:
Alternatively, you can return to the file manager and upload the missing external reference to the same location in the file manager as the parent file.