I've just set up an account to confirm I'm experiencing the same 'hidden SSID' behaviour on the Vigor2763ac with firmware: 4.4.5.3_BT

I've contacted support as it appears to be a bug but they keep sending me a link to a knowledge article on hiding the SSID and filtering clients by MAC address.

Does anyone know how to successfully raise this as a bug with DrayTek support?

I see this too on my 2865ac. I suspect it's a backhaul Network for Mesh nodes. I have exactly the same thing on my TPLink based Mesh WiFi LAN and they use hidden networks for its backhaul between nodes.

EDIT: I just upgraded my 2865 to 4.4.5.3RC2a and can confirm the hidden networks are gone.

Funnily enough, that's the closest I came to resolving it - a Google search where someone mentioned mesh backhaul. When checking my 2763ac the mesh was disabled so I hit a dead end.

Is there release candidate firmware for the 2763ac that's publicly available?

Mesh was disabled on mine too.....but I suspect the bug that was alluded to earlier was them being present despite Mesh not being enabled.

I would contact support and asked for the latest RC release for your 2763. 

Will do. Thanks for the info, very much appreciated 

Where do you get .4.5.3_RC1_BT (or RC2) from do we have to ask Draytek Support