Cannot modify header information – headers already sent

I see a lot of these PHP Warning in the logs:

PHP Warning: Cannot modify header information – headers already sent in […]/wp-content/plugins/wild-apricot-login/Modules/Core/Session/Manager.php on line 20

Where a setcookie() call is made apparently late in the game. Is there a possible fix for this, or should I just continue to ignore the messages?

13 public function __construct($sessionName, $expirationTime, $expirationOffset)
14 {
15 $this->expirationTime = $expirationTime;
16 $this->expirationOffset = $expirationOffset;
17 $this->setSessionParams($sessionName);
18 $this->data = new WA_Modules_Core_Session_Data($sessionName . ‘_’ . $this->sessionId, $expirationTime);
19 $this->setExpiration();
20 setcookie($sessionName, implode(self::DATA_DELIMITER, array($this->sessionId, $this->expiresIn)), $this->exp>
21 }