Thank you for your help.
So I did a flight check like in the article to determine the profile here is the result : https://ibb.co/ftKHzG8 It seems that there are multiple color spaces in this file. I tried viewing it in all the profiles I had and couldn’t see the problem in any of them. When opening the document in illustrator though, I found Stroke overprint on all the parts that produced the weird result. https://ibb.co/2vwnPMm
I just don’t know how to avoid this in the future. I can’t open every pdf I get in adobe, followed by illustrator, followed by photoshop until I find a problem.
How do you export your files to print ? do you have a preset you would recommend to avoid problems in the future ? I suspect my export preset is the source of the problem but I can’t be sure.