Due to a software issue with one LNS in to the network (the gateway between your router and the internet), when there is a higher load on the device, latency will increase.
This has been identified and the manufacturer is involved to provide a resolution.
We are attempting to spread users out against other gateways but a reconnect will also do this should you be on the affected gateway.
Update: A fix has been received and planned maintenance will mean this applied. For the moment, we have rebalanced the gateways and steering sessions away from the affected hardware. If you are seeing the above issue, a reconnect will resolve the problem in the immediate term.