thanks for the suggestion. I have not tried this yet, but will report back once I do. I have about 50,000 photos in the catalog, and am worried this may take too long.
What I have done so far is to work around this by hiding some of the panels which I usually have displayed. This forces the program to regenerate previews, and they come out fine. This is faster then having to zoom in, wait for 1:1 to be generated, and then zoom out and wait for the new preview to be generated.