Warning: Header may not contain more than a single header, new line detected in Symfony

I am getting a header error in all pages. More specifically:

Warning: Header may not contain more than a single header, new line detected in Symfony

Kind of lost at what is causing this problem. Haven't been able to figure it out so far. Any help or direction is greatly appreciated.

============ERROR LOG================
Warning: Header may not contain more than a single header, new line detected in Symfony\Component\HttpFoundation\Response->sendHeaders() (line 337 of /vendor/symfony/http-foundation/Response.php) #0 /core/includes/bootstrap.inc(548): _drupal_error_handler_real(2, 'Header may not ...', '/home/...', 337, Array) #1 [internal function]: _drupal_error_handler(2, 'Header may not ...', '/home/...', 337, Array) #2 /vendor/symfony/http-foundation/Response.php(337): header('X-Frame-Options...', false, 200) #3 /vendor/symfony/http-foundation/Response.php(371): Symfony\Component\HttpFoundation\Response->sendHeaders() #4 /index.php(20): Symfony\Component\HttpFoundation\Response->send() #5 {main}.