UPDATE: Still not fixed after reinstall…but I may know why
As I started writing this and re-read Shuji’s reply, I realise where I went wrong/what the next steps are. I uninstalled Zwift (via add/remove programs), then rebooted, then reinstalled. When reinstalling Zwift noticed I already had a Zwift folder in Program Files, but I told it to install anyway. Once installed I didn’t need to login again and all devices were still connected. I’ve just completed ToW Stage 2 (Cat B - Standard) again and still no dino costume or big wheel.
So, next step is to properly delete all traces of Zwift on the uninstall (as per the link Shuji supplied). Rushed it somewhat last time and no doubt some traces left in remaining folders.
…at least I got in some extra miles, even though they were hillier than I’d have liked
EDIT: Possibly unrelated but the Companion App wasn’t working as expected on this ride - it could tell I was in an event, but didn’t show the usual HUD style display