I have CiviDiscount set to offer a discount to members on an event price set. This is working fine.
However if the event registration uses Paypal Standard and the user goes through to the Paypal payment form but then clicks the Cancel link there, when they return to the event registration form, it shows full price: the discount is no longer automatically applied. The user has to go to the registration form afresh, losing their edits, in order to get the discount back.
Not sure whether this will need fixing in CiviDiscount or in core. I've posted an issue in the CiviDiscount issue queue: https://github.com/civicrm/org.civicrm.module.cividiscount/issues/223 . Also posting here for a wider audience & opinion.
CiviCRM 5.13.4, CiviDiscount 3.1, 3.3 or 3.7, Drupal 7
Also replicated on current dmaster.