Quick update from Sky: they're still investigating but notice that when it fails, IPv6 goes down completely and the PS5 stops being able to call home. They're trying to find why, and whether it's a symptom or the cause of the BT Sport app error.
I can't seem to find an option to turn off IPv6 on the PS5, but if you have the option to turn it off on your Sky router then that could be worth a try - nothing to lose by trying.
Note: I've passed on the observations here that disconnecting and reconnecting the network immediately before playback sometimes helps.
OK, so the good news is that Sky have now confirmed that there's an issue with IPv6 on the Sky router and their dev team are working on it.
Disabling IPv6 from the router settings will resolve this issue, but this is done at your own risk - it may cause issues with other services or devices on your network.
@DarrenDev Just caught up on the thread as I am having the same problem. Do we know or have an idea of when we will be updated from sky? I don’t want to have to turn off the IPv6 on the router incase there are issues caused elsewhere
I can confirm that having disabled IPv6 on my sky hub has resolved the issue. No devices in your house will be using IPv6, this is rarely used and mainly only in use for large enterprises, so disabling it for a home router will not have an effect on your devices.