Hi @Michael_Appleton-Web. Welcome to Forums This is Juan from Zwift. I appreciate you taking the time top share your issue here.
I understand how important it is for you to add each meter to your total to complete the Everest Challenge. I took the initiative to check your account and noticed that the closest activity to 1370 m is Zwift - The Pretzel in Watopia, which was ridden on March 28. This activity shows 1,363 m reached.
It appears that you’ve logged into the Zwift app on different devices. This could have caused this unexpected behavior. Anyhow, the right path to solve this is to contact our support channel. Therefore, I encourage you to contact us. We will be happy to assist you.