Replying to my own question. OK. Found it. Make sure your scanner is on. Go to System Preferences > Printers & Scanners
If you've been using your scanner before the update, then you should see your scanner in the left-hand sidebar. (If not, you'll have to add it.) Click on Open Scanner. It will scan, but I would rather not have to go to System Preferences to scan every time!
Solution - use application Image Capture, a default Mac app which should be in your Applications Folder. Drag it to your Dock. You will find your scanner under Devices. VOILA!
It's not the same Epson Professional scan window I'm accustomed to using. It's now a part of Image Capture. The Scan interface is much cleaner.