Android One Device Can't Connect to Core Windows 10 PC

@support
I’m a new subscriber. One feature that sold Roon to me was the ability to control Roon on my core W10 PC with my the Android app on my Android phone. Everything worked fine while trialling the service on the PC and Android app. 2 days ago, my subscription payment went through - and now it’s not working! What the hell is going on?!

Details:
Core device: Microsoft Surface Pro 2 w/ 8GB RAM / 256GB storage / using Seagate 1TB drive to access library of FLAC files.
Android Device: Nokia 8 Sirocco running Android One (same OS as Google Pixel 2).

All was working fine until today, then for some reason my android app can no longer connect to the Core. I’ve gone through all the advice on the help section of the app. The Android app is seeing the Core Device - it says “Connecting”, and then “Connection Failed”. Obviously something has changed either in Windows 10 or the Android app since yesterday.

Please could you figure this out and advise. Without the remote app functionality I’m not really sold on the Roon experience - so will be asking for a refund if this can’t be resolved.

Thanks for your time

Nemo