Thanks Pop,
Though I'm still struggling to understand what's going on . . .
Is it my server provider firm, or is it visitors who are using Nginx (whatever that is) who are triiggering the errors?
I think I need to get in touch with my sever company and see if they can shed any light on it.
I wouldn't normally bother, but as I say, hundreds of megabytes of bandwidth are being lost for some mysterious reason.