This happened to me once, and it was a combination of:

1) Three seats were declared inoperative (The AVOD was not working), even though this was the 787-10's first passenger service.
1a) If passengers were sitting in seats that had inoperative AVOD, then the FAs need to perform manual demonstration, at least in the impacted cabin.
2) The family of 4 were ahead of me on the upgrade list, but only 3 inoperative seats were available, so they declined the upgrade.
3) The GA did not make a second pass for the next 3 people on the list, which I suspect was due to lengthy explanation needed from point 1, and they needed to close the door.

Write it in, and you might get a voucher. Keep it straight forward and focus on the fact that first class upgrade was not processed - the first upgrade to PP is not relevant.