I'm looking at my IFX on AmigaForever (to help someone else on a different problem).
I just looked inside the IFX icon. (tool types)
that is, I right clicked and opened the icon (information)

I have mine set to
WINDOWED

NOW, this will make IFX open on whatever screen you happen to have but one reason I like this is that it tends to reduce problems. Anyway, if you have it set to something else, comment it out with brackets () and type in WINDOWED.

see if that works

if not, you can also type in
DEBUG

and see what results. I haven't done this in a million years but I think the debug file gets saved to ram.