WordPress was recently updated in the usual automagic way for my sites to version 4.9.3, a general bug squashing release, with no urgent security fixes.
Unfortunately, a bug slipped into the bug fixing, which means that automatic updates have been broken.
The newly released 4.9.4 will sort this out, but you’ll need to click the update link in your Dashboard to get it. This update does nothing other than making sure that the next point release will allow automatic updating.
Details from the usual place.