The new Diagnostics feature points to the URL https://docs.particle.io/support/troubleshooting/common-issues/p1 when a device is not connected (the TROUBLESHOOT CONNECTIVITY button as seen below).
For Photon, this leads to the LED Codes page in the Photon documentation: https://docs.particle.io/support/troubleshooting/common-issues/photon
Will probably be a dead URL for the new devices also?
J