There's only a few different platforms that internet radios use but its unlikely several radios would all be using the same one - over time some platforms don't keep up with all broadcaster changes which can be a downside to internet radios.
Devices like Sonos or Amazon Echo are more app based - for example the BBC Sounds app - so they possibly might outlast other radios. But if this was the issue they wouldn't connect at all - to lose connection on just one service after hours/days is pretty unusual - and if it happened after changing router that's significant.
To test from a PC I'd use the BBC Sounds player - found next to iPlayer via a web browser - and see if that's affected at the same time. There's also a BBC Sounds app on the phone or things like TVs or streaming devices.
For when issues happen I think it's always worth having another router to hand - either to try instead of the ISP router connected to the ONT (or copper) - or with DHCP disabled and connected by LAN to the ISP router and used as an Access Point to which devices connect over WiFi instead of connecting to the ISP router.
If it was a change of ISP rather than router that caused it, and trying the BBC sounds app or a different router doesn't help, then it could be a lot harder to fix - though other EE users would likely have noticed something like this.
