Lost 3 of my 4 Comcast email accounts

I use all 4 of the four email accounts offered by Comcast. I have been using Xfinity's wb email, but over the last few months, I have started to see the following error message: "The provided login data to access mail server imap.comcast.net seem to be wrong. Please correct them."

It started with one account I almost never use. I tried checking all the settings for the account, and they were identical to my main account. I ignored it.

Now 2 more accounts give the same error. All folders and, I assume, saved emails, are missing. My main account still works but I fear it will also go tits up.

I had not done anything or made any changes to the settings. They are as they should be.

What the heck is going on and how can I fix it?