I've been on that 'ghost train' before, by chance, and I posted about it at the time because I didn't know it was possible for a train to traverse West to East through Brighton like that.
What is totally shameful is how they are missing the obvious trick of advertising it as a Falmer train at...
Has it ever been that bad?
There just didn't seem enough capacity and trains weren't being filled completely.
I'd imagine some folk arrived at Brighton Station in decent time and missed kickoff.