@Andy_Shuttleworth you can disregard the version message on Zwiftalizer. The latest version numbers sometimes differ depending on which OS you’re using, and Zwiftalizer is assuming the latest numbers are all the same.
More importantly, are you seeing any spikes in the network chart? If they happen mid-ride, the symptom is that all the other avatars disappear.
If it happens while you’re saving the session, then it might result in the session not saving correctly.