I’m having this issue too. I’ve viewed the offer several times since receiving it in December. We have a trip planned in July with a bounce back offer and thought about doing a split stay using the emailed pin offer on the second hotel stay. I went to view the rates last week and got the same message you did. I couldn’t find an expiration date anywhere in the email but there may be one in some fine print somewhere.
We have decided not to do a split stay. But if we were, I would call to ask for a cast members help with using the discount, if it was still valid.