I have put everything together as it was. The ones with black insulation tape are the ones that use to be live I labelled them days before the problem occurred.
I checked each wire individually and they are holding firm, not loose. The downstairs light works, the upstairs one does not.
With a torch I checked for any extra wires in the boxes and pull cord switch (a hole where the single 1.5mil wire comes out) but there isn't anything else.