Opening a file in Indesign to edit, blurry images/pages

Hi, beginner Adobe user here who does not use InDesign often - I have a source file with a deck that I need to edit. When I open the file in InDesign, there are a few pages that are extremely low quality. I have a PDF to compare to, so know that it was clear at one point. It was created by someone else who I am no longer in contact with so I can't ask them to make new edits.

I know some of the images and assets need to be re-linked, which I am able to for most, but for some of the pages, the images or spreads look absolutely fried and do not even let me link/re-link any assets (e.g. the title page image is not selectable, so I can't even replace the asset).

I checked for locked layers as well. Am I missing something here? I think some of the assets were made previously in Photoshop, but I was not given any photoshop files along with this deck's source folder. Could this be a reason for the quality? Thanks for any help!