Apps can only be updated when signed into the same account that was used to get them in the first place. If you are signed into either the device or the store with a different account and your device is set to update apps automatically, this can explain what you are observing.
What you are seeing can happen if instead of simply changing the email address used for an account as described in this support article Change your Apple Account primary email address - Apple Support you instead created a brand new account. If this is what you did, go back and change the address correctly.
Alternatively, it is possible to be signed into the Apps & Media Purchases setting with a different address. This commonly happens if you let another person download an app on your device. In that case you have to delete the app and download it using your account. This may result in data loss but you have no option.