When an image is exported to PDF with Bicubic Downsampling selected, the interpolation creates a a column of pixels which seem to be duplicated from the column immediately preceding it. This isn't very noticeable on full images, but on specific cases, like the round circle attached, it creates an unsightly "bump out" that alters the shape of the circle.
This does not occur if Average Downsampling is selected, so that's the immediate solution to the problem, but maybe the ID team needs to look at how Bicubic Downsampling is applied and if there's any way to improve this interpolation.
As mentioned, it also affects full images, but the "repeated" column, while there, is not an EXACT replication of the one to its immediate left, so the interpolation is using a set of samples slightly differently, but still very close to a duplication.
The effect also seems to occur on the last row of pixels, but not in the same way, but still creates a sense of a flat spot on the circle example.