I’ve had my Arteon for a year now and again today (third time) I’ve seen my MPG really low.
I drive in eco mode but have noticed that when cruising it stays in gear (I.e. E3 rather than E).
Has anyone else had this issue?

If I were you, I would go to a car service. There can be many variants of what the problem is, and you yourself will think for a long time, so it's easier once to go to the service and understand what the problem is. I can advфise a mot history check. It's a pretty good company, they can help you. I think so.

Thank you for your suggestion! I appreciate your advice to go to a car service and get a professional opinion on the problem. It makes sense to save time and let the experts diagnose the issue accurately. I'll also look into the mot history check service you mentioned. Your input is valuable, and I'm grateful for your help!