Presumably at some point it had an issue which required it to wait for components, and in the meantime other components stripped to keep the others in traffic. Before long, getting it back together and in traffic is a much bigger job. With the arrival of the 322s, the fleet had more slack so there was no rush... until now with refurbishment coming up, getting 009 back in traffic releases a unit to be worked on.
It's not that unusual for the odd unit in a fleet to become a "Christmas Tree", including relatively modern fleets such as the 333s.