Invalid SSL certificate : Certificate is for web.mysite.com, not 178.xxx.xxx.xxx (moved from help)

When I click on the "Open Webmin" button in Cloudmin of my monitoring server for any of the managed systems, I get an error:

Invalid SSL certificate : Certificate is for web.mysite.com, not 178.xxx.xxx.xxx

I just noticed this recently. Previously everything was working correctly for a very long time. This happens both for the servers with self-signed and Let's Encrypt certificates. Everything else works good, server status is displayed correctly for all the servers managed by Cloudmin.

Anybody has an idea on why this happens?

P.S. I moved the topic from the Help section to here.