Express.js, apollo-server Playground, Route error "Not found" but it works

Question

I have a problem with my express app:

https://glitch.com/edit/#!/enthusiastic-velociraptor

When I navigate to GET /graphql it gives me Playground but in console I have a Not found

Why?

Reproducible with these steps:

• go to: https://glitch.com/edit/#!/enthusiastic-velociraptor
• see the code and open console
• go to: https://enthusiastic-velociraptor.glitch.me/graphql
• Graphql Playground works but in console you have "Not found" error!