It is responding correctly based on the height of the slider. Mobile screens are different aspect ratio than desktop/laptop.
You could try changing the height of the slider on mobile with this custom CSS, added to ‘Appearance‘ > ‘Customize‘ > ‘Additional CSS‘:
@media (max-width: 768px) {
#home-slider-section .bx-viewport,
#home-slider-section .slide {
height: 300px !important;
}
}