QuickAccess in Windows10 Explorer is quite handy for pinning often-used folders. Recently mine stopped working for some reason. It would not show the items previously pinned, nor would it accept new pins.
After a bit of searching, the fix is:
In CMD as Admin:
del %appdata%\microsoft\windows\recent\automaticdestinations\*
del %appdata%\microsoft\windows\recent\automaticdestinations\*
