wp-admin do not show comment

I have function for avatar in functions.php

if(!is_admin()){
	add_filter('get_avatar', 'site_get_avatar', 10, 5);
}else{
	add_filter('get_avatar', 'site_get_avatar_admin', 10, 5);
}
function site_get_avatar($avatar, $id_or_email, $size, $default, $alt){
	$myavatar=get_field('user_avatar','user_'.$id_or_email);
	if($myavatar){
		return $myavatar;
	}else{
		return get_template_directory_uri().'/img/avatar.png';
	}
}
function site_get_avatar_admin($avatar, $id_or_email, $size, $default, $alt){
	$myavatar=get_field('user_avatar','user_'.$id_or_email);
	if($myavatar){
		return "<img width='40px' src='".$myavatar."' />";
	}else{
		return "<img width='40px' src='".get_template_directory_uri().'/img/avatar.png'."' />";
	}
}

when this code is active , in wp-admin comments not showing anythings but when disable this code , show all comments