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?

Below picture shows you the example 'frame in frame' state along with supported structure in indesign layer.

Find "Supported Frames and Content in InDesign" here