I was asking the same myself few minutes ago as far as I experience 522 constantly and I cannot choose “enviroment” when adding a route for it on one domain 
While it’s working normally on “preview” tab, but not working neither when I open the “worker URL” in a new tab.
I managed to get some “cf wayback machine URL” one time - then it showed the page content as it should be.
Thanks for feedback @Walshy