Hello @Nigel_Harker welcome to Zwift forums.
Shuji at Zwift HQ here. I peeked at your server logs and see that you are using Zwift Play controllers. Play controllers only have one shift paddle per side, much as SRAM levers do. So the Play controller only offers two options: sequential-style (the default) or SRAM-style.
The controllers that come with the Zwift Ride smart frame have two shift paddles per side, just like Shimano levers. For “Shimano-style” shifting to be possible, you need two per side. Hope that makes sense?