Created a separate thread for you since your post was originally in a GasTracker thread.
Few questions to ensure we're on the same page.
1. GasCubby isn't directly connected to a specific Apple ID. Did you change your ID because you no longer have access to that email address?
2. Is that ID the same address you used to originally Sync your data?
3. When was the last successful sync performed?
4. When did your data disappear? Did you update/reinstall/some other action prior to it vanishing?
Here is the history of my problem:
I changed my Apple ID after I purchased the Gas Cubby.
1. Because of that I can't update Gas Cubby with my new Apple ID account on my iphone.
2. I still use the same email address for my Apple account.
3. I had a successful sync about a month ago.
4. Cubby icon disappeared due to the problem with installing ios 8 and that disabled the sync temporary.
After fixed the ios8 issue and try to sync with iTunes to get my Gas Cubby back,
I got a message: "The app "Gas Cubby" was not installed on the oPhone because you are not authorized for it on this computer."
But after I authorized this computer and still got the same message,