The above refers to problem with only Avast One and only after importing Settings. This problem doesn't exist in Avast Free. Avast Shredder is a Premium feature while I used free version, so it is disabled. So I don't think it is problem with Shredder.
I found the cause of this problem. Restoring settings from an earlier version of Avast One, and then restarting the PC, cause external hard disks to be treated as flash drives without Recycle Bin after they are unplugged and inserted later.