I've just upgraded to CiviCRM 4.7.31 from 4.7.30 on Drupal 7 and we've identified an issue which wasn't there previously. After being redirected to PayPal from a contribution form, the session is invalidated once you return to the site. I've checked the qvKey from the form to the "return page" (which throws an error) and it is correct. Payments are lodged correctly. Any ideas?
Error log is
$backTrace =
#0 /www/sites/all/modules/civicrm/CRM/Core/Error.php(381): CRM_Core_Error::backtrace("backTrace", TRUE)
#1 /www/sites/all/modules/civicrm/CRM/Core/Controller.php(833): CRM_Core_Error::fatal("We can't load the requested web page. This page requires cookies to be enable...")
#2 /www/sites/all/modules/civicrm/CRM/Core/Controller.php(853): CRM_Core_Controller->invalidKeyCommon()
#3 /www/sites/all/modules/civicrm/CRM/Contribute/Controller/Contribution.php(74): CRM_Core_Controller->invalidKeyRedirect()
#4 /www/sites/all/modules/civicrm/CRM/Core/Controller.php(312): CRM_Contribute_Controller_Contribution->invalidKey()
#5 /www/sites/all/modules/civicrm/CRM/Core/Controller.php(204): CRM_Core_Controller->key("CRM_Contribute_Controller_Contribution", TRUE, FALSE)
#6 /www/sites/all/modules/civicrm/CRM/Contribute/Controller/Contribution.php(55): CRM_Core_Controller->__construct("CiviContribute", "null")
#7 /www/sites/all/modules/civicrm/CRM/Core/Invoke.php(304): CRM_Contribute_Controller_Contribution->__construct("CiviContribute", TRUE, "null", NULL, "false")
#8 /www/sites/all/modules/civicrm/CRM/Core/Invoke.php(84): CRM_Core_Invoke::runItem((Array:15))
#9 /www/sites/all/modules/civicrm/CRM/Core/Invoke.php(52): CRM_Core_Invoke::_invoke((Array:3))
#10 /www/sites/all/modules/civicrm/drupal/civicrm.module(445): CRM_Core_Invoke::invoke((Array:3))
#11 [internal function](): civicrm_invoke("contribute", "transact")
#12 /www/includes/menu.inc(527): call_user_func_array("civicrm_invoke", (Array:2))
#13 /www/index.php(21): menu_execute_active_handler()
#14 {main}
perform
method: github.com/civicrm/civicrm-core/pull/11708/commits/…