I don’t know whether this is expected behaviour or a fault …
Take a 24mpx file in TIF format, and select “focus” as the function - Sample TIF and mask a small area - in my case, the left hand flower, then try to save … it seemed to be taking a long time, so I went to the kitchen, cooked and ate my lunch … still running … went back to the kitchen and made a cup of espresso (including the time to weigh and grind the beans) and drank it … still running (by now, well over an hour on a 6 processor i7 laptop with a GTX 1060i card), so I pulled the plug.
Out of curiosity, I exported the file from DxO PhotoLab as a 97%, 300dpi, full size JPG - about 6mb - masked the same area and focus-sharpened - took 1min 30 secs to save.
So, is this expected? Or should I say “to be expected”? I prefer to work in 16-bit TIF if an image is passing through several different apps. I have another project where some 50K bit wide panorama is likely to end up going into gigapixel so I can print it several metres wide and one high …