So far i think it has happened to me twice. Not sure if anyone else has faced this issue? From the chatbox, you can see I did not receive any rewards after exiting portal.
Did you get warped out when you received that message, or did you drop items to make room in your inventory, and try again, after having received that message?
Actually, this should be fixed now. Sorry for the inconvenience caused, and thanks for reporting the issue!
I had this issue occur to me today - don't think it's resolved. I had at least one slot available in all my inventories, the portal let me through, and then I received no rewards or messages that I had completed the event.