"time machine couldn't complete the backup" near "error occurred while copying files" mojave
I get the error "Time Machine couldn't complete the backup to "drives name".
"An error occurred while copying files..."
Time Machine suggested using Disk Utility to repair the backup disk. Disk Utility gave the disk a clean bill of health (as well as for the SSD in my wife's MacBook Pro). The laptop is running 10.14.6 (18G95). What is the problem and what is a fix?