Histogram shows no clipping but the image has red highlight warnings

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I can't figure out why this is happening. I am currently running LR Classic v 10.3, but was having the same issue in at least the one prior version. The histogram shows absolutely zero highlight clipping, gray triangle, but the image itself has red areas with clipped highlights, and indicates individual channels when I press ALT+Highlights. Do I believe the histogram or the image? This is happening on both raw files as well as images I've edited in some of the Topaz plugins. Most of the time moving the highlights slider all the way to the left is not enough to resolve it. Often I have to dig deep in the tone curve to resolve all of it and by the time I've finished the image looks awful, but sometimes just moving the Point Curve output down to 254 will take care of it. But that still doesn't answer the question about why the histogram says everything is fine but the image disagrees. Help?