Not working for you? Could be any number of reasons.
Interactive f/g extract, does definitely reset using linux gimp 2.10.6 and gmic 2.3.6
Using Windows, all I have for testing is a basic Windows 10 64bit Virtual Machine.
I did find gmic_gimp_qt 3.3.6 'buggy' so went to 3.4.0 testing. That pops up error messages as well, but could well be my Win 10 VM that is the problem.
However, resetting the control points in Interactive Foreground Extract does work.
A quick video demo: 1 minute 40 seconds:
https://youtu.be/szCR2UEDCK4Edit: Went back to check Windows gmic_gimp_qt 3.3.6 again.
A clean up
Removed existing gmic_gimp
deleted ...roaming/gmic folder
deleted gimp pluginrc file.
Used the Windows installer version of gmic_gimp_qt.
Looks ok now. no error message. Maybe a bad setting in the gmic folder.
Resetting the interactive f/g extract, works same as video.