Updating to 10.13.4 seems to have solved the problem. FWIW, I used the Combo updater. I have always used the incremental updater before this. I don't know if there is any relationship, but all seems to be OK.

Jon

macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365