TIFF image exported from a PDF in Acrobat Pro is unreadable by Acrobat Pro

I regularly use the Export Image -> TIFF and then Combine the TIFFs to absolutely flatten a PDF.  Today I find that Adobe Acrobat Pro can no longer read its own exported TIFF files.  Did a recent update cause Adobe Acrobat Pro to write out corrupt TIFF files or make its Combine function fail to properly read the TIFFs it has written out?