Cannot connect to Roon Server/Core

Core Machine

Mac MIni (late 2014)
Version 10.14.6 (18G3020
2.6 GHz Intel Core i5
8 GB 1600 MHz DDR3
Runs as headless machine, connected to Naim Uniti Atom

Network Details

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Audio Devices

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Mac mini is connected to network via Ethernet (network running fine)
Outputting to Naim Uniti Atom via network
Atom outputs to Macintosh Integrated amp
Library held on QNAP 251+, also connected via ethernet to network.

Library Size

Library approx 200 albums - 2000 tracks

Description of Issue

Roon Server runs on the Mac mini and has done on and off for several years.
Hasn’t been used for a few weeks.
Tried to connect yesterday by using Roon Remote on iphone 7 and could not connect.
Remote finds Roon, it flashes “choose your roon core” (less than a second, too quick to select) then moves to the Roon logo ‘pulsing’ on the screen. Thats it.
Tried connecting via MacBook Pro, same process.
Installed Roon on a differnt Mac Mini and same outcome. Managed to take this screen shot…

So, summary is that an Iphone remote, MacBook pro and Mac mini all sharing same network cannot connect to Roon Server.