When using inastamask on a light image, sometimes Dark 3 throws up a totally black mask. This happens, but far less frequently on the other dark masks.
Clicking on a brighter or darker mask then comes up good, and going back to Dark 3 gives a proper mask.
Possibly I notice it on Dark 3 more because tend to start there.
That's a strange one and the first report of this behavious. Please keep an eye on when it happens and take note of what buttons/steps were pressed before the black mask appears. Then drop me an email and I will look into it.
Sure thing mate.