wwwolf on "[Plugin: Wordfence Security] Scans on several sites stopped working on 25 June"

Using WordFence (free)
I have a variety of live sites on different hosts, with different combinations of plug-ins. On some I have moved wp-config.php outside the web-accessible tree, on others not.
Scheduled scans on many of them (but not all) stopped working around the same time - on June 25th. The log lists the first line: "Scheduled Wordfence scan starting at ... (etc)" but gets no further, on scheduled or manual scans. Looks like the next line should be "Contacting Wordfence to initiate scan" so guessing it's failing to make contact?
I did not update or changing anything that day, and on my favourite host (Rochen) several have stopped, but one is still working OK. I can see no pattern with regard to the plugins I'm using.
Did anything change that day? I tried checking the box to start all scans remotely, but that didn't help either. Any ideas...?

https://wordpress.org/plugins/wordfence/