This HP has been a mess for a week now. Originally it was the Coztic Itzel Belongings HP, which bugged repeatedly- I attempted it several times, but the mobs liked to get lost in the floor and despawn so it was impossible to complete.
When the tweak patch changed it to the Pact Airship Wreckage, though, it still showed as available on the map in the original location of the Coztic Belongings (see mouseover on the map in the screenshot), but the Place of Power gives the “you’ve already earned these” message (see on-screen dialog in the screenshot).
The Hero Point tally for the fullscreen map also shows that I have 8 of 11 complete, with this as one of three still available.