@Igor,
1. I am using Epson Scan and Epson Scan driver. I have the latest versions of these installed.
2. To be sure, I have today downloaded same from Epson support website and reinstalled both Epson Scan 3.772 and Scan Driver 3.773, but I had these versions before.
3. Following this software install and restart, I am now able to scan a page, save pdf file, rename and delete without it being taken prisoner by avast.
So appears last update version of Avast has somehow interfered with the Epson scanner software. Re-installation of that scanner software has fixed my immediate problem, unless it comes back to haunt me later.
I dont know if the other poster @samdobrow can resolve his same problem by doing a similar reinstallation of whatever scanner software he is using.
PS. I have no files with filenames like unpXXXXXXXX.mdmp in C:\ProgramData\AVAST Software\Avast\log.