Just as an update in case anyone has similar issues, I completely disassembled the kit and tested each strip individually. One long strip seemed to not light up completely but then did so I reconnected everything and now it works except the bottom strip, which sometimes works, sometimes doesn't. Which I assume was up the top (2nd in the chain) the first time I had it all connected so when it was playing up the last 2 strips which were connected after it also failed.
Anyway, I've arranged for a replacement set so hopefully that resolves it.