Nextcloud "503 Service Not Available" after DietPi update

I’ve been running Nextcloud on a Pi3 for a couple of months (using lighttpd) for a couple of months, replacing an ancient laptop running Owncloud and all has been working well (aside from some ongoing issues getting my letsencrypt cert to renew, but that’s a different problem) and when I noticed there was a dietpi update available I applied the update.

However since this time I have been unable to connect to Nextcloud.

The root web site works and I see the placeholder page, but when I try to connect to the Nextcloud URL it returns a “503 Service Not Available” error. Rebooting the Pi hasn’t made any difference.

When I try to use the Android app it reports “Server in Maintenance Mode”.

I’d be grateful for any assistance getting things back up and running.

Many thanks is advance.