PNG from Illustrator placed in InDesign exports badly in PDF?
For your case in indesign, just expand your frame and the flat parts will be gone, the resampling causes the circle edges anti-aliasing to extend outside of the default bounding box.
Working for a company with a circular O in the logo, I've had to deal with the downsampling issue quite a bit. The 'flat tire' is an issue that frequently occurs when others try to use our logo and try to resize it.
Prior to Photoshop CC (where you are working with instances of files) when dropping in an .EPS, then free transform scaling it after it was rasterized, almost every time it would flat-tire. The way to avoid it was to import the EPS at the exact final size you needed it into your PS document. I found myself guessing the dimensions and re-importing the EPS many times over as a workaround to keep the 'tire' pumped up.
Unfortunately Adobe hasn't yet discovered the secret to resampling a smooth circle when resizing it...