"Not a diagram file" error when opening file from GitHub

[TheNinth7]

Hi,

I am trying to convert a Visio file to drawio and store it in a GitHub repository. The Visio file opens just fine in https://app.diagrams.net, and I can save it to my GitHub repository. However when I then try to open it up again I get the error "not a diagram file":

When I click on any of the two .drawio files, I only get this error:

Any suggestion what I could be doing wrong?

[davidjgraph]

What is the file suffix for the file being opened?

[TheNinth7]

The suffix is .drawio

[TheNinth7]

When I download the file from GitHub and open it from my local hard drive, then drawio opens it just fine. Only opening via GitHub leads to the error shown above.