It appears your file has failed due to low resolution elements. I would suggest downloading and checking your Advanced file report. On this Advanced file report you will be given a visual indication as to what elements have failed due to resolution.
If the element that is highlighted isn't an actual image and is vector or a drop shadow/transparency, in your InDesign PDF export settings, under advanced, make sure Transparency Flattener is set to high. If the highlighted element is an actual image, check the actual resolution in the file report, then upsample the image to the correct resolution and re export your file.