Okay, so after last Save step of the LRT 4.x Visual Workflow (Previews/Deflicker) we're instructed of course to return to LR CC and "read metadata from files". Fine, this has always worked just perfectly in the past. Now, suddenly if I perform the LRT Save routine and return to LR CC to update the metadata changes for deflicker, I cannot – the menu will be greyed out (even tried selecting just a single frame, a few frames, all frames again, but no joy) However, if I choose a different collection of photos and then just switch back to the LRT managed photos, the "read metadata from files" menu comes back to life. I struggled with this "hang" for hours before I figured it out!

When one of the images is orphaned in Lightroom (deleted from the harddrive but still in the Lightroom catalog), Lightroom will not allow you to read the meatdata for the whole sequence. Check that - right click on the folder, then "Synchronize" normally sorts this out.

Wow, now that I think of it, I'll bet that's exactly what happened. I believe I might have deleted one or two of the first images. Thank you for the quick response!