For no apparent reason, the website’s content stopped appearing today, and for no apparent reason it is now reappearing.
When it was still not appearing, I deactivated all plugins else than GP’s, as suggested. As expected, the website’s content reappeared. I then reactivated each plugin one by one, making sure to check which one was causing the issue. To my surprise, none of them does. Go figure.
I have the feeling that I will come back sooner than later with this same issue.