Clipped button doesn't receive touch input
You should move your FAB Z index in the layout to be on the top of the other views in the screen, so when the touch event occurs the FAB should receive the touch event before another views.
and to understand why it doesn't receive touch events in the bottom part of FAB, that because you did use android:clipChildren="false" so actually the parent bounders is smaller than that but the draw happens out side it, so when the touch event is received to the parent first then it tries to divert it to the desired child, and the touch event must be within parent bounders, so the bottom part of FAB is outside the bounders of the parent, and the touch event is not for him.