Thanks for getting back to me, David. This is indeed the same site.
On further investigation, it seems that the page is only having trouble loading whilst a backup is taking place. My current theory is that the server may be having trouble with the load, or we’re hitting PHP memory limits or something like that. The only nagging thought is that other pages load fine while a backup is running.
I’ve also noticed a warning that Updraft has encountered a very large file. There seems to be a wp-snapshots folder which contains a file that’s over 1GB (looks like someone else had installed the duplicator plugin at some point). I expect this isn’t helping matters, so I’m going to remove that.
John