I would be extremely annoyed.

Gold status should have made a difference in my opinion.

I can't, however, see how you managed to get through conformance all the way to the EDI gate with a boarding pass for that flight only to be told
you had no seat on that flight

Whenever this has happened to me (with short T5 to T5 connections) I have been stopped at conformance and given a new boarding pass for my later flight, so it has been straight to the lounge rather than try and make my original flight which is closing or has already closed without me.