Why are PDFs look blank in Acrobat

For context, I work on a Mac, and I've had these PDF's for a month or so - reading them, highlighting info, making notes and comments, etc. A few days ago, I noticed that when I open PDFs in Acrobat, they look blank. If I have text highlighted in the document, the highlight is visible but not the text. I've tried to open them in Illustrator and Photoshop to check if they are corrupt or anything like that, and even they appear normal. The issue seems to be in Acrobat. As mentioned, I've been working on these PDFs for weeks, so I can't afford to lose them. Please advise on how to fix it.

I've attached screenshots to show what I mean - the one that it looks like in Finder before I click it open, and the other is what it looks like in Acrobat. 

Ps. I'm aware that this is an issue many other Mac users have and I've tried so