I've managed to get the issue to go away!!
It seems Sky Go doesn't like something about my ISP, because if I turn on Cloudflare WARP client, which is essentially a proxy server between me and the internet, the constant error messages stop and I can stream once again.
I use YouFibre as my ISP, which has a slightly different architecture to most ISPs in that customers are not directly connected to the internet, have no external IP address, and are essentially just a device on a network being allocated an internal IP from a DHCP server; like any traditional network albeit on a large scale. More ISPs are going to be heading down this route in the coming years, due to the shortage of IP4 addresses and slow switch over to IP6, so Sky really need to sort whatever issue the app has with it.
Cloudflare WARP client is free, so maybe download it and give it a go.