If you try to access the CropTool by the link https://croptool.toolforge.org/, it would either endlessly show a load bar:

or it would show the interface with a message that the server returns 504 error, and nothing happens after the button "Connect" is pressed:

or, maybe, after some time after pressing "Connect" it would yield a timeout error:

During all of that, such a message appears in the browser console: