I've now had pretty much the same response
"Thank you for contacting BBC iPlayer support.
I understand you have contacted us because when you watch the live stream of the World Cup on iPlayer, at some point it will jump to another channel, or it may jump back two hours. Hopefully, I can help with this.
We have spoken to the iPlayer television team who have confirmed that this device doesn't have live restart functionality enabled. We have disabled this feature on the device as it was failing to restart.
This is a known issue with this Humax device. We have raised it to them, but unfortunately we don't have an ETA on when this will be investigated on their side.
I hope this has helped, thanks again for contacting us."
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I wasn't trying to restart, I was trying to watch 'live'. This has not been disabled otherwise I would not have been able to press a button marked 'watch live'