Background image isn't fixed on Mobile

OK the issue is because of the height of your logo, do you have a smaller logo for mobiles ? If yes i can provide you a workaround

Ok, so this is going to need a bit of tinkering from your end :), i hope you created a child theme, if not create one now and copy the header.php file from the theme fodler to child theme folder, edit line 59 as below
CHANGE FROM

<h1 class="logo">
							<a href="<?php echo esc_url( home_url() ); ?>">
								<img src="<?php echo esc_url( $logo ); ?>"
								     alt="<?php bloginfo( 'name' ) ?> | <?php bloginfo( 'description' ) ?>">
							</a>
						</h1>

TO

<h1 class="logo">
							<a href="<?php echo esc_url( home_url() ); ?>">
								<img src="<?php echo esc_url( $logo ); ?>"
								     alt="<?php bloginfo( 'name' ) ?> | <?php bloginfo( 'description' ) ?>">
							</a>
						</h1>
						<h1 class="mobile-logo">
							<a href="<?php echo esc_url( home_url() ); ?>">
							<img src="YOUR_MOBILE_LOGO_IMG_SRC_HERE" />
							</a>
						</h1>

Once you make the above edit, time to add some CSS, add the below css in the child theme style.css file

@media (max-width: 768px){
	.logo{
		display: none;
	}
	.mobile-logo{
		display: block;
	}
}
@media (min-width: 768px){
	.mobile-logo{
		display: none;
	}
}

Let me know if you still see any issues