Thanks Barry.
Tried a full re-install and restart but that doesn't seem to have fixed the problem
I'm wondering now if it is specific to the file itself, or to a particular computer. The file has this issue on a couple of computers here, but not mine, and other files work OK for everyone. On one of the machines where it did not work we got an "OpenGL has been disabled" error message (attached).
So in summary:
Computer no. 1 - No OpenGL in any file
Computer no. 2 - No OpenGL in one file, OpenGL OK in other files
Computer no. 3 - OpenGL OK in problem file and all others too.
Maybe this discussion should be moved somewhere else, as I now don't think it is related to the update.