Down to a basic theme as there’s something, somewhere in the depths of my site, breaking the database and affecting other sites on the same server. I feel rather bad about this. It doesn’t seem to be caused by any of the obvious plugin candidates, so I’m leaning towards it being some odd code in the theme. Hopefully. I’ll strip and revamp my main theme (actually I may just start again, given how messy it’s become over the past couple of years).