Cheers for the detailed response. What a rubbish implementation. It's basically unusable.
I'm hoping the TradingView integration includes SB and the problem is fixed there.
There are other UK brokers which offer futures, but their platform/charting isn't as good, however they do display the historical data. At the moment I'm thinking about flip-flopping between two, using IG when enough data is there, then going through the other one when it's not. It's really not ideal but I only trade a handful of markets so it's doable until one of the brokers does it all.
"You'd be better off looking at the charts of real futures." Yep the price can be different. Candlesticks, timeframes, it can all get a bit wonky.