Invalid argument supplied for foreach()

Logging the following warning: Invalid argument supplied for foreach() in /Users/alexgorski/Code/jbfc/mainsite-wp/public/wp-content/plugins/meta-box-columns/src/Processor.php on line 73

The value of meta_box[columns] is 12 instead of the expected array. This started happening when I upgraded to 1.2.9 (from a much older version) and is still occurring with 1.2.13.

Here is log and offending function:

[16-Aug-2021 14:59:07 UTC] PHP Warning:  Invalid argument supplied for foreach() in /mainsite-wp/public/wp-content/plugins/meta-box-columns/src/Processor.php on line 73
[16-Aug-2021 14:59:07 UTC] printing meta_box[columns]
[16-Aug-2021 14:59:07 UTC] 12

/**
     * Fetch and store column data from meta box.
     */
    protected function parse_columns() {
        if ( empty( $this->meta_box['columns'] ) ) {
            return;
        }
        foreach ( $this->meta_box['columns'] as $key => $column ) {
            $this->columns[ sanitize_key( $key ) ] = $this->parse_column( $column );
        }
        error_log("printing meta_box[columns]");
        error_log($this->meta_box['columns']);
        $this->has_columns = true;
    }