Cumulus Support

....since the 25th October. Very strange. I've been running the site, using the basic Cumulus templates, for six years, with few issues.

Well after spending an afternoon fiddling with Kaspersky Firewall and the Cumulus ftp settings to no avail I happened to uncheck "Use active FTP mode" and, bless me, everything fired up and the website is now updating.

Can anyone explain?

The normal setting for FTP is "passive". It is possible your hosting provider allowed "active" connections for some reason, and then withdrew the facility hence why only "passive" would work as the default setting.

Suggest you ask your hosting provider what they changed.