Viewing tif files in Preview, Dropbox

I've created two image files in Photoshop, removing hidden layers, merging layers, and then flattening the layers, saving them as tif files. One is about 4 MB; the other is about 24 MB.

The 4 MB files shows up fine in QuickView and in Preview; the 24 MB file shows up with a white background and one element from one of the layers.

I've also tried this saving the 24 MB tif file in layers, preserving the alpha; same result.

Uploaded to Dropbox, both tif files show up with only one layer visible, even though the file has flattened all the layers!

Thanks for any help you can offer sorting this out. I'd like to be able to view the 24 MB tif file in Preview.