When Webmin loses connection with the sever the connection error message appears in its red box. Clicking the 'x' in the top right corner to make it go away does not work because the window just pops right back almost instantaneously, unless perhaps the connection has been reestablished but once gone it typically won't be regained unless the browser refreshes the page. This is a major annoyance when one is composing an email. Once a connection error occures, one loses access to the message text box as the connect error message blocks the UI and steals focus away from everything in the background. This results in all work on the email to that point being lost.
Stefán, hi.
This issue has been fixed in the latest 19.09 release of the theme tgst is ready for inclusion for upcoming Webmin 1.880.
You csn also update to tge latest version using theme's configuration.