v3.8.11 causes crash on event reg pages

I get this error and backtrace (on Civi 5.71.2). It doesn't happen with 3.8.10, I'm going to try to see why shortly.

Error: Typed property CRM_Event_Form_Registration::$order must not be accessed before initialization

CRM_Event_Form_Registration->getPriceFieldMetaData (/home/jon/local/mysite/web/sites/all/modules/civicrm/CRM/Event/Form/Registration.php:97)
Civi\FormHelper->getPriceFieldMetadata (/home/jon/local/mysite/web/sites/all/civicrm-custom/extensions/org.civicrm.module.cividiscount/Civi/FormHelper.php:68)
Civi\FormHelper->getPriceFieldOptionIDs (/home/jon/local/mysite/web/sites/all/civicrm-custom/extensions/org.civicrm.module.cividiscount/Civi/FormHelper.php:82)
cividiscount_civicrm_buildForm (/home/jon/local/mysite/web/sites/all/civicrm-custom/extensions/org.civicrm.module.cividiscount/cividiscount.php:130)
CRM_Utils_Hook->runHooks (/home/jon/local/mysite/web/sites/all/modules/civicrm/CRM/Utils/Hook.php:276)
CRM_Utils_Hook_DrupalBase->invokeViaUF (/home/jon/local/mysite/web/sites/all/modules/civicrm/CRM/Utils/Hook/DrupalBase.php:73)
Civi\Core\CiviEventDispatcher::delegateToUF (/home/jon/local/mysite/web/sites/all/modules/civicrm/Civi/Core/CiviEventDispatcher.php:314)
Symfony\Component\EventDispatcher\EventDispatcher->callListeners (/home/jon/local/mysite/web/sites/all/modules/civicrm/vendor/symfony/event-dispatcher/EventDispatcher.php:251)
Symfony\Component\EventDispatcher\EventDispatcher->dispatch (/home/jon/local/mysite/web/sites/all/modules/civicrm/vendor/symfony/event-dispatcher/EventDispatcher.php:73)
Civi\Core\CiviEventDispatcher->dispatch (/home/jon/local/mysite/web/sites/all/modules/civicrm/Civi/Core/CiviEventDispatcher.php:263)
CRM_Utils_Hook->invoke (/home/jon/local/mysite/web/sites/all/modules/civicrm/CRM/Utils/Hook.php:168)
CRM_Utils_Hook::buildForm (/home/jon/local/mysite/web/sites/all/modules/civicrm/CRM/Utils/Hook.php:495)
CRM_Core_Form->buildForm (/home/jon/local/mysite/web/sites/all/modules/civicrm/CRM/Core/Form.php:783)
CRM_Core_QuickForm_Action_Display->perform (/home/jon/local/mysite/web/sites/all/modules/civicrm/CRM/Core/QuickForm/Action/Display.php:76)
HTML_QuickForm_Controller->handle (/home/jon/local/mysite/web/sites/all/modules/civicrm/packages/HTML/QuickForm/Controller.php:203)
HTML_QuickForm_Page->handle (/home/jon/local/mysite/web/sites/all/modules/civicrm/packages/HTML/QuickForm/Page.php:103)
CRM_Core_Controller->run (/home/jon/local/mysite/web/sites/all/modules/civicrm/CRM/Core/Controller.php:355)
CRM_Core_Invoke::runItem (/home/jon/local/mysite/web/sites/all/modules/civicrm/CRM/Core/Invoke.php:323)
CRM_Core_Invoke::_invoke (/home/jon/local/mysite/web/sites/all/modules/civicrm/CRM/Core/Invoke.php:69)
CRM_Core_Invoke::invoke (/home/jon/local/mysite/web/sites/all/modules/civicrm/CRM/Core/Invoke.php:36)
civicrm_invoke (/home/jon/local/mysite/web/sites/all/modules/civicrm/drupal/civicrm.module:470)
menu_execute_active_handler (/home/jon/local/mysite/web/includes/menu.inc:527)
{main} (/home/jon/local/mysite/web/index.php:21)