Here is a new article we have about this problem:

Images in referenced files do not plot in AutoCAD for Mac on Mac OS 10.12 (Sierra)

There is no ETA yet on when an update will be available to fix Sierra compatibility issues, but AutoCAD will notify you as soon as it is available. If your computer is mission critical for AutoCAD and none of the workarounds suggested in the article help, then I would suggest using Time Machine and rolling back your system to what it was before Sierra.

Bryce Thelin
AutoCAD Product Support