src/DataContainer/ColumnSet.php
public function getAllTypes()
    {
        if ($GLOBALS['TL_CONFIG']['subcolumns'] != 'bootstrap_customizable') {
            return array_keys($GLOBALS['TL_SUBCL'][$GLOBALS['TL_CONFIG']['subcolumns']]['sets']);
        }

        $this->import('Database');
        $collection = $this->Database->execute('SELECT columns FROM tl_columnset GROUP BY columns ORDER BY columns');

        $types = array();

        while ($collection->next()) {
            $types[] = $collection->columns;
        }

        return $types;
    }
public function getAllTypes()
    {
        if ($GLOBALS['TL_CONFIG']['subcolumns'] != 'bootstrap_customizable') {
            return array_keys($GLOBALS['TL_SUBCL'][$GLOBALS['TL_CONFIG']['subcolumns']]['sets']);
        }

        $this->import('Database');
        $collection = $this->Database->execute('SELECT columns FROM tl_columnset GROUP BY columns ORDER BY columns');

        $types = array();

        while ($collection->next()) {
            $types[] = $collection->columns;
        }

        return $types;
    }
Replace subcolumns getAllTypes method to load all created columnsets.

There is a fallback provided if not bootstrap_customizable is used.

@return array

@SuppressWarnings(PHPMD.Superglobals)