WordPress, ipn/extern.php: Call to undefined function get_option() in CRM_Utils_System_WordPress->getTimeZoneString()
Since CiviCRM 5.11.0, the PayPalIPN is trying to get the timezone from the
CRM_Utils_System_WordPress which is not available until WordPress is bootstrapped.
At this point, as Joomla Drupal and Backdrop are all bootstrapped in the
extern/ipn.php script in master & 5.15, it seems the obvious solution is to always call
CRM_Utils_System::loadBootstrap before running the selected
$paypalIPN class. I'm also not sure why Joomla would need the user loaded, which is the difference between the Joomla and Drupal/Backdrop calls currently available.
Agileware ref is CIVICRM-1228