Disappeared where? On Screen or in Print?
First, check the story editor to see if the anchored object is really there or not. The icon for the anchored image is circled in red in this screenshot:
Next, is the image anchored inline, or is it a custom? In the second screenshot, the same item has been moved outside of the print area, although it is still anchored to the same bit of text.
All layers are on
@Annie – this is not relevant, because anchored objects ("inline" or "custom" makes no difference) are tied to the layer of their parent text frame.
1. The objects could be "hidden".
There is a contriol for that to bring back all hidden objects on a spread:
alt + cmd + 3 (for InDesign on Mac OSX)
2. The objects could be set to "No Printing" and you look at your document with the "View / Overprint Preview" checked. You can control the "No Printing" in the Attributes Panel.
3. A combination of 1. and 2.
4. The objects are removed…
Could happen with a TEXT or GREP search/replace action that happens to include all anchor characters in your text.