Is there more information regarding this issue?

Steps to reproduce the issue: 1 - Install the extension 2 - Open the extension and it reads the cookies as supposed 2 - Fully quit safari 3 - Open safari 4 - Open extension and it can't read the cookies 6 - Go to safari > develop > web extension background content and clicked on the corresponding extension 7 - Open extension and it starts to read the cookies as supposed to

I've ran this from xcode and testflight. This only started happening for safari 18 (it worked for 17). I've installed some similar extensions from the store and I've noticed that they have the same issue. Also, if I inspect the website I can see that the cookies have persisted.

Thanks for your answer. I don't think this is related because the code works fine for 17.5.

thanks, I have just reported this on feedback assistant.