Hi Rikard, thanks for picking up on this for me. A couple of observations since I posted this in the forum.

I managed to get the site back on line after a complex series of “trial and error” attempts, disabling many plugins and restoring from backups. At one stage I deleted the parent theme and reinstalled it, that deleted all the formatting (as I detailed in my original post) but at least it got the site back. I had taken a site backup when I first recognised the issue, and I found that restoring that backup actually worked too. However, I think it worked only because I had disabled many of the plugins and turned off the preloader in the theme settings.

Once the site was back I created a staging copy and systematically activated the plugins again. Everything seemed to work fine, and the last thing I did was to turn the preloader back on. On the staging site that worked, so I did the same on the live site and once again all I got was a spinning preloader on all pages. Deactivating the plugins, turning the preloader off and purging the cache (along with lots of swearing and luck) brought it back again.

So, I wonder if it’s somehow linked to the preloader, and maybe conflicts between the theme and the other plugins. The site is hosted on SiteGround and their SG Optimizer plugin also handles caching, minimising HTML/CSS/JS etc. I did have WP-Optimize installed but deleted that in preference to SG Optimizer – I wonder if that’s part of the problem? Currently most of the front-end optimisation is turned off in the SG Optimizer plugin.

The site seems stable right now, so I’m REALLY nervous to try too much without support. If you need, I can create a staging copy for you as well. Credentials for the live site are in the Private Content.

Many thanks Rikard.