This has happened to me to as well.
My error log says “PHP Fatal error: Can’t use function return value in write context in /home/ataloholdings/public_html/wp-content/plugins/advanced-custom-fields-pro/includes/local-fields.php on line 304”.
When I go to that file and comment out the function ‘acf_have_local_fields’, the site is now visible, but none of the custom fields are available in the backend of the pages, and my error log now says ‘Call to undefined function acf_have_local_fields() in /home/ataloholdings/public_html/wp-content/plugins/advanced-custom-fields-pro/includes/acf-field-functions.php on line 346’
