The same frequency separation method I've been using, and teaching,
for the last several years, no longer works in the latest version.
This is the same method taught on this YouTube video:The Amazing Power of Frequency Separation Retouching in Photoshop - YouTube
have tried a work around method, which involves using an Add instead of
Subtract in Apply Image and inverting it, I have tried a hard reset and
deletion of the Photoshop preferences, both did not help.
My colleague has version 19.1.0 and worked just fine.