It will try fetch feeds with file_get_contents() instead of using simplepie

custom-feed-reader.php

<?php
/*
Plugin Name: Custom Feed Importer
Plugin URI: https://premium.wpmudev.org/
Description: It will try fetch feeds with file_get_contents
Author: Panos Lyrakis @ WPMUDEV
Author URI: https://premium.wpmudev.org/
License: GPLv2 or later
*/

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

if ( ! class_exists( 'WPMUDEV_Custom_Feed_Importer' ) ) {

	class WPMUDEV_Custom_Feed_Importer {

		private static $_instance = null;
		var $feed_urls = array();

		public static function get_instance() {

			if( is_null( self::$_instance ) ){
				self::$_instance = new WPMUDEV_Custom_Feed_Importer();
			}
			return self::$_instance;

		}

		private function __construct() {

			$this->feed_urls = array(
				'http://siteone.com/feed/',
				'https://sitetwo.com/feed'
			);

			add_action( 'wp', array( $this, 'maybe_shcedule_job' ) );
			add_action( 'wpmudev_feed_schedule', array( $this, 'fetch_feeds' ) );

		}

		public function maybe_shcedule_job(){
			if ( !wp_next_scheduled( 'wpmudev_feed_schedule' ) ) {
		        	wp_schedule_event( time(), 'daily', 'wpmudev_feed_schedule' );
		    	}
		}

		public function fetch_feeds(){

			foreach( $this->feed_urls as $feed_url ){

				self::fetch_feed( $feed_url );
			}

		}

		public static function fetch_feed( $feed_url = null ){

			if( is_null( $feed_url ) ){
				return;
			}

			$feed_content = file_get_contents( $feed_url );
			self::import_feed_content( $feed_content );

		}

		public static function import_feed_content( $feed_content = null ){

			if( is_null( $feed_content ) ){
				return;
			}

			$x = new SimpleXmlElement( $feed_content );

			foreach( $x->channel->item as $entry ) {

				if( get_page_by_title( $entry->title, OBJECT, 'post' ) ){
					continue;
				}
		       	
		       	$new_post = array(
		            'post_title' => $entry->title,
		            'post_content' => $entry->description,
		            'post_status' => 'publish',
		            'post_type' => 'post'
		        );

		        $post_id = wp_insert_post( $new_post );

		        if( $img = $entry->enclosure->attributes()->{'url'} ){
		        	if( self::is_valid_image( $img ) ){
		        		$attachment_id = self::import_image( $img );
		        		if( $attachment_id ){
		        			set_post_thumbnail( $post_id, $attachment_id );
		        		}
		        	}
		        }

		        
		    }

		}


		public static function is_valid_image( $img_url = null ){

			if( is_null( $img_url ) ){
				return false;
			}

			list($width, $height, $type, $attr) = getimagesize( $img_url );
			$allowed_image_types = array( IMAGETYPE_PNG, IMAGETYPE_JPEG, IMAGETYPE_GIF );
			return isset( $type ) && in_array( $type, $allowed_image_types );

		}


		public static function import_image( $img_url = null ){

			if( is_null( $img_url ) ){
				return false;
			}

			$filename = @end( explode( '/', $img_url ) );

			$uploaddir = wp_upload_dir();
			$uploadfile = $uploaddir['path'] . '/' . $filename;

			$contents= file_get_contents( $img_url );
			$savefile = fopen( $uploadfile, 'w' );
			fwrite( $savefile, $contents );
			fclose( $savefile );

			$wp_filetype = wp_check_filetype(basename($filename), null );

			$attachment = array(
			    'post_mime_type' => $wp_filetype['type'],
			    'post_title' => $filename,
			    'post_content' => '',
			    'post_status' => 'inherit'
			);

			$attach_id = wp_insert_attachment( $attachment, $uploadfile );

			$imagenew = get_post( $attach_id );
			$fullsizepath = get_attached_file( $imagenew->ID );
			$attach_data = wp_generate_attachment_metadata( $attach_id, $fullsizepath );
			wp_update_attachment_metadata( $attach_id, $attach_data );

			return $attach_id;

		}

	}

	add_action( 'plugins_loaded', function(){
		$GLOBALS['WPMUDEV_Custom_Feed_Importer'] = WPMUDEV_Custom_Feed_Importer::get_instance();
	}, 10 );

}