HI Mike. Thank you for your offer of assistance, however there no longer seems to be a problem. That is, I can no longer replicate the problem. Very strange. Before reporting it, I replicated the problem repeatedly while trying various alternative file formats. Just now, while preparing to respond to your offer I reduced the size to 1028 pixels max dimension of one of the TIFFs that had been causing the problem, exported it using Affinity Photo2, and then tested it before replying. To my astonishment, there was no problem. So I tried the original full-size TIFF (a 45 Mpixel beast; exported from Capture One v22. Again, no problem. So I tried another TIFF I knew had caused the problem initially. Again, no problem. As a final check, I quite Publisher and reopened it and immediately tried one of the original TIFFs. Still no problem. I have no explanation, but there is absolutely no doubt whatsoever that when I first tried with Publisher 2 earlier this morning, there was a problem that could be replicated. I did not restart the OS; the only thing that changed to my knowledge is that Carbon Copy Cloner is no longer running its backup in the background; I doubt that has anything to do with it. Anyway, I no longer have a problem, for whatever reason. Thanks again for your offer.