Website icons are missing on my favourites

Hello,

Not sure if anyone can help me. I've seen a few solutions for this however they are all outdated now.

I have a handful of websites in my bookmarks/favourites section on Safari. Including well known sites such as Facebook, Google, Twitter etc.

However I've noticed that a few of them down have the icons for the website. No idea why because when I visit the site you can see the icon on the tab.

Anyone know how to restore them so they all appear and don't have ones missing?