just tested cv.jit.floodfill on Windows and it seems to work fine. are you running the version from the Package Manager? feel free to send me a patch demonstrating (on or off list) if so inclined.

i've also problems with the cv.jit.floodfill object on Mac (didn't test it on Windows). Did you find an alternative or solution? see my topic with a patch which is crashing on different mac's: https://cycling74.com/forums/jitter-crashes-help-with-reading-crash-report

And yes @Rob i did installed the latest version from the package manager