This isn't a spectrum issue, it's an ESPN issue.
To me, it appears that the problem is that ESPN bypasses the Spectrum credentials page, and automatically grants an invalid authentication for Spectrum users. I emailed ESPN support today and received this reply:
Thank you for reporting this issue to us.
We are aware of the issue and are working to resolve it as quickly as possible. We apologize for any inconvenience.
We have a ticket open for this issue. Unfortunately we do not have a timeline as to when this will be completed.
For live assistance with this or any other issue, please call Customer Care at 1-888-549-3776 (ESPN) between 9:00 a.m. and 1:00 a.m. EST.
ESPN.com Customer Care