Unexpected device in Spotify iOS app devices menu

[user-removed]

Plan

Premium

Country

UK

Operating System

iOS

My Issue

Issue observed in November 2018.

It has been reported to me that a device is unexpectedly appearing in the Spotify iOS app devices menu.
I am interested in finding out about any known circumstance under which this may occur.

Steps that may reproduce:

1. On one network, switch on and connect a Marantz SR5009 AV Receiver (via WiFi) and a non-Marantz client (via ethernet).
2. On another network, open the Spotify iOS app and access the devices menu.

Expected behaviour:

The Marantz SR5009 AV Receiver and the non-Marantz client are not in the devices menu.

Reported actual behaviour:

The non-Marantz client is in the devices menu.