I think that I’d try connecting it to the router with an Ethernet cable, and see if it shows up then. If it does, I’d submit a diagnostic and either post the resultant number here, or call in to Sonos.
One other thing...this morning I triggered on your statement “literally next to the router”. Generally speaking, to avoid WiFi interference, you’d want at least 18 to 36 inches between the two devices. Not convinced this would solve the issue, but probably worth mentioning.
Moderator note:
In addition to the above, if you are looking for information as to what causes a Blinking Orange light to appear on your Sonos devices, there are a number of things that could be going on. The first thing to do would be to review this article here, which talks about what the different coloured lights on Sonos products mean. In my experience, it generally means the device is struggling to obtain an IP address. In these cases, unplugging the router for a few seconds tends to remedy this.
No luck? Try wiring it into your router via Ethernet. Does that then work? Try unplugging the Ethernet cable (without unplugging the speaker from power).
Does it drop off the system again after you do this, or does it not connect at all via cable? At this stage it would be wise to contact our care agents via telephone.