Seems ajax in the new version of Zimbra is very very slow over a 128kb adsl connection. I host a mail server but my upline is only 128kb. Internal network Zimbra works fine.
There were no issues with the last version of Zimbra, ajax worked fine over this line speed. Error message attached.
The HTML works fine just the AJAX client does not work.
Browser used Firefox 188.8.131.52 (error attached) and similar error with internet explorer (fails to load).