In general, due to this wrong layer structure in InDesign, images show up as low-resolution while check-out.
When you will get frame in frame state ?
Usually you will get this state when you copy existing placed image and paste it into new image frame using "Paste Into" (Alt+Ctrl+V) option.
How to find frame in frame in InDesign layers?
Red arrow in the above image represents frame in frame which is not supported.
Green arrow in the above image represents right one.