KMail will not retrieve mail - server address changed

My ISP changed the email server address. I made the requisite changes in Kmail. The server settings are POP3, SSL/TLS port 995. When attempting to retrieve mail, I get the error message

Unable to login to the server "".Could not login to
The server terminated the connection immediately. 

Kmail sits on “preparing to send” forever before I receive the error message. According to the ISP, the login attempt does not even appear on their system log. It is as if Kmail does not even attempt to reach the host. It is not the ISP. I put the account into Thunderbird which has no problem reaching the account and downloading email. The Thunderbird settings are the same as I mentioned in KMail with “normal password”. I’ve been using plain in Kmail, but have tried cleartext and login with no luck. I could switch to Thunderbird, but have been using KMail for years and prefer it. I’m using KMail 5.19.0 (21.12.0) on Frameworks 5.88 and QT5.15.2.

Any help would be appreciated.

One more piece of information: Kmail will retrieve from my Gmail account which is IMAP. My other accounts are POP3. I originally retrieved GMail using POP3 and that broke when I had to change my password. I deleted that account from KMail and added a new GMail account using IMAP which then worked. By the way, I tried deleting my other accounts and adding them anew with POP3 with no luck.

Is POP3 broken in KMail???

AFAICS, only if a mixture of IMAP and POP3 accounts are configured – haven’t got around to writing a Bug Report …

On further research, the problem seems to happen with secure SSL/TLS accounts. It does not seem to occur with non-SSL accounts. Could I have bad keys or something like that? If so, is there a way to refresh them? I’ve tried deleting the account and then adding it and that doesn’t seem to work.