Test and fix a routing / caching issue resulting in "This site can’t be reached" error.

I manage a web platform and I have encountered a strange problem - on loading of any address beyond the base domain, the page will only load if using F5 + ctrl. If loaded without only F5 ( a simple refresh ) then the error is given: "This site can’t be reached...."

That is what is happening on the surface.

I hope someone recognizes this error and knows the fix.