There is no chance that the hack attempts on her customer Paypal account would be due to CBSubs. All Paypal sensitive data stays on the Paypal website, that's the main reason of using a payment processor.

Wondering how your customer could count hack attempts on her Paypal account. Paypal does not communicate such internal statistics. It could be even a phishing attempt email that she got from a hacker which claims that. Who knows.

Regarding your error log, it could be a silent notice which is unrelated to CBSubs. But hard to say without seeing details of one of those notices. You can click on each and see full details. The path of the files in the call stack usually helps you finding the "culprit" part.