PHP 7.1 incompatibility with HighEnd THeme

I have Highend Version 3.6.2.

When my site upgraded the PHP to 7.1, my pages displayed an error. I had Siteground take me back to an older PHP version so that it would not occur but wanted to know what I need to do to make it compatible with the latest PHP.

This is what siteground emailed me to pass along to you:

After updating the PHP version of the server, I am getting the following error on the website:

Warning: Parameter 2 to wp_hide_post_Public::query_posts_join() expected to be a reference, value given in /home/xrayvsnc/public_html/wp-includes/class-wp-hook.php on line 288
Can you please check the incompatibility?

I looked to see if there was any update to my HighEnd Theme but there is none.

Thanks.