Check if the drawing is locked (if the project is in a file sync project) if it is not, save is not allowed of the dwg file.

If a drawing that is unlocked in a sync project (Cloud file storage) is opened a question will appear: "Open Drawing(s) The following drawings are not locked: (Drawing name(s)) Do you want to lock them before continue to open?" (Yes/No)

The new change is that if "No" is selected you can not save it. This applies to changes made with IMPACT and pure CAD (lines etc.). 

Save as still works because it is not an IMPACT drawing anymore.

Save when it is not a cloud storage project works.

When the file is locked it also works.