Intermittent error “This page doesn’t seem to exist” when the page does exist

For a very long time now I have been getting the Intermittent error "This page doesn't seem to exist" when the page does exist. It goes away after a refreshes or waiting a while. I'm not the only one who gets it, and it's not on just one page, it's different every time.

I have CloudFlare CDN and WP Rocket for cache. I think it is one of those, and I'd be surprised if I am the only website that experiences this problem. However, searching on the internet got me nowhere but articles explaining a 404.

Does anyone know anything about this or has experienced this?

TIA