Using an Apple MPB mid-2014 and MacOS 10.12.6, I can mount any number of USB thumbdrives. The drives appear as mounts on the Desktop, but no longer appear in a Finder window under the Devices section. They used to do so.
The devices are visible via the command line as mounted filesystems under /Volumes. The
diskutil utility may be used to mount or unmount them. Similarly, they appear on the Desktop and may be ejected from the right-click menu.
The Finder preferences to show external mounts in Finder windows has been selected.
I have tried using DiskUtility to repair disk permissions. No errors were discovered.
Does anyone know how to repair the system state so that mounted USB devices appear in the Finder windows? Thanks!