Cannot turn off distracting items in Private Browsing

I regularly use a website in Private mode on Safari. It has an annoying set of instructions which pops up in the page when you start. I used "Hide distracting items" to bypass this, but I have found that the website does not work without it.

When I close the web page and restart it, the hide items setting persists and I heave to manually chooses show distracting items every time.

Has anyone else come across this?