The hyperlinks in Scapple need to be clicked three times to open. The developer believes that this is necessary due to technical reasons.
In fact, you can trigger the middle mouse button to open using Keyboard Maestro actions (can be set to be effective only in Keyboard Maestro).
The key point is to use the Keyboard Maestro action "Extract hyperlinks from styled text (rich text)":
Open the hyperlinks in Scapple with one click.kmmacros (14 KB)