In regards to your concern on which the API returned null for the name of your specific account, it seems that there is something weird happening on this account. If you'll check the new AdWords UI, this account doesn't have any account name. Normally, in the left side of the AdWords UI on where you can see your clientCustomerId, the top of your clientCustomerId should be your account name. However, in this account, I could not see the account name. You can verify this on your end by logging on this account and compare this with your other accounts.
This is unusual since you cannot create an AdWords account without the account name. Also, can you confirm if you used the AdWords UI or AdWords API in the creation of this account before? So I can also better check that this is indeed the issue, can you provide your SOAP request and response logs via Reply privately to author option?Furthermore, since this concern is more on the product level as both UI and API have null values for the account name, and not AdWords API specific, can you also post this concern in the
AdWords Community Forum for further assistance on why this specific account does not have an account name on it?