No longer able to stream to Musicast speakers "Can't play this right now"

[M_F_K]

Plan

Premium

Country

Australia

Device

Windows + iPhone

Operating System

Windows 10 and iOS 13.4.1

My Question or Issue

Spotify seems to have lost its ability to stream to the Musicast devices I have which has been working fine for a couple of years now. There are two devices that are connected by LAN cable, the other 4 are WiFi and all of them say 'Can't play this right now' on both my iPhone and my desktop Spotify apps. It can't be a problem with the LAN/WiFi as they can all stream FLAC files I have on ym desktop without any issue or skipping.

Any idea why this may have started happening?