I have same issue but I think the email is working but can be slow due to TWC horrible email system. I made no changes when this cropped up a couple of weeks ago . On another post I was given settings to check or change, did not help. Does same thing on other computers that were working also prior. I think TWC changed something.

Have been back to Spectrum. Found they no longer have a single IP address for the email servers. They run multiple servers and use Dynamic IP addressing. They have changed the server name (IMAP and SMTP) to mobile.charter.net. Correcting the name eliminated receiving the popup: The current operation on 'inbox' did not succeed. The mail server for (my account) responded: Unrecognized command: ID. However now receive popup: Mail Server Password Required. My password is always rejected. Offered a place to change password but, it does not change. Can use their webmail: https://webmail.spectrum.net/mail/auth and it works with my password. So Spectrum considers their system is OK and problem is with Thunderbird. Maybe so but, not sure how Thunderbird would interfere with the login at Spectrum. So, would someone at Thunderbird contact someone at Spectrum and, together, resolve the problem. Thank you!

See this post for Spectrum/Charter/TWC/Roadrunner etc.:

https://support.mozilla.org/en-US/questions/1275842

My setting are ok, as mentioned above if I try the mobile.charter address my password is rejected.