I backed up my MC29 library and selected the option to save thumbnails. I then installed MC30 and restored the library that I had backed up from MC29. What didn't get restored were the thumbnails (24 of 6291 came across). Was there an extra step required? In any event I just opted to rebuild missing thumbnails. All but 89 were rebuilt within 5 minutes. Exited MC30, restarted and re-ran build missing thumbnails and the last 89 were built.
Nothing else seems amiss.
thanks