FINALLY found a solution to this that works (for me at least) having tried most of the original suggestions.

Before upgrading, I'd created a junction from c:\windows\installer to another drive to save space on my SSD. When I looked, this junction still existed from the c:\windows.old\windows folder, but not from the active c:\windows\installer.

By copying the files from c:\windows\installer to my folder on the other drive, then creating a new junction, all the icons came back (some required a restart to refresh).

Hope this helps others with the same problem.