Safari reloads bookmark icons upon every restart
I realise a "me too" is not helpful, but I wanted to keep the discussion alive. This is the first post I have found on this subject after several attempts. So, good to know I am not alone.

Unfortunately, the answer from Geek is only a work-around. I work a lot on my Mac with a data plan and I like the favourites tiles / icons on my new tabs.

However, this does not happen on all Macs. I have a much-older MacBook air where this does not happen in High Sierra, but on a more recent MacBook Air I do see this every time.

The main difference between these machines, is that the one that has this issue is configured as a work Domain account, or in other words, as a Mobile device.