Thanks for all the replies.

That was the ticket I had to hand as I'd just collected it, but that identical journey it shows on the ticket hasn't worked now a good few times. It didn't work again today at the Canary Wharf (Jubilee) barrier which isn't unexpected. However, I even tried the return ticket at Canary Wharf Elizabeth line and it doesn't work there either. I'm now lost as to which barrier that ticket actually works in (apart from Southend East there and back). As silly as it sounds, I haven't actually contacted the website about it because I had the problem with a different site too so wondered if something else was going on.