After changing the Canvas size (not artboard), saving and compressing a PDF makes all images blurry

Hi

TLDR: After changing the Canvas size (not artboard), saving and compressing a PDF makes all images blurry while the file size is still rather large. It was able to be compressed better before changing the canvas size.

I have been working on a huge brochure for a client and have been using Illustrator. I started to run out of space on my Illustrator workspace (Canvas) and had to create a new Illustrator file to increase the canvas size.

I transferred all my artboards (by copying and pasting the artboards) across to the new file and it seemed to be working fine while working on it. The only issue is when I save the file as a PDF and add compression, it becomes extremely blurry while still having a rather large file size (100's of megabytes). Here's an example below:

Before transferring the files to this new and larger Canvas size, the compression worked well and the images kept their quality. I've even tried saving the images as an uncompressed PDF and used a different compression tool but have found that this also makes the images extremely blurry and pixelated. This method seems to work on my older file before changing the Canvas size, so I am convinced it must be this change to the new Canvas size that is causing the issue.

My goal is to create a decent-quality editable PDF that is compressed but is still decent quality while working on a larger canvas size. We want to be able to compress the file like it did before changing to the new Canvas size. Is there a way to do this without these compression issues? Has anyone else had this issue?