Wondering if there was any update on this? Any testing I can do to help narrow things down? Not affecting me but would be keen to get to the bottom of this.
Unfortunately doesn't seem like there's anything else we can do, Vodafone staff have stopped replying to the issue on the community forums aswell. So far it seems like a QoS issue on the router. I suspect it has to do with the router deprioritising "gaming" to reserve badwidth for Vodafone TV, something that's being pushed heavily when upgrading to fibre, would explain the missing QoS toggle in the router settings too if Vodafone wants their online TV service to always run smooth.
Besides encrypting your traffic through a VPN or buying a 3rd party router there doesn't seem to be anything we can do.