When I use the columns shortcode, I get a PHP Warning.

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The columns shortcode uses regular expressions to intelligently determine your columns without the need to identify each column’s index. This requires the use of the PHP pcre package, version 7.8 or later. The following error:

PHP Warning: preg_match_all(): Compilation failed: unrecognized character after (?<

indicates that you are running an older version of pcre. To solve this error, upgrade your server’s pcre package. You can contact your hosting provider for specific details.