Spent the reasonable amount of money to get an actual cassette for my Zwift and Hub and magically my shifting works the same as when I’m actually riding the bike. Wow, who would have guessed. My mistake was trusting Zwift to send me the right cassette, which they didn’t, and even if they had got it right, the chances of it being 100% smooth with my actual drive train would have been sketch. This is why the serious smart trainers (Wahoo, Elite, etc.) don’t even try and let you get that for yourself.
Honestly, I wouldn’t buy a Zwift Hub a second time, but I’ve already taken the hit on depreciation so I’ll wait until I drop to 70 kilos to reward myself with a Wahoo instead (and sell this one for whatever I can get for it, if not just give it to one of my sons to try out).