Orb Vallis Narmer excavation-titled bounty reward bug

[(PSN)Astralwanderung]

I can't remember the exact name of the bounty, but it was about excavation, and its 5th phase was an excavation.
Thing is, even if you do a "perfect bounty" (getting all bonus objectives in each phase, including the last), the last phase is not considered "perfect" and the bounty doesn't give the bonus reward.
At first I thought that Orb Vallis instance I was in was glitched, but even after I exited and re-entered it kept happening each time.
When the excavation phase ends, right after the "bounty completed" message, Eudico says that one of the excavators was destroyed, even if they were all at full health. This happened each time, so I guess the problem is something along the line of the excavators despawning just an instant before the mission ends, and thus they're considered destroyed.

Each time I was in a party, so there were three excavators, I don't know if this would happen even by playing solo, which could mean having only a single excavator (but I don't think so, since it's phase 5 of the top bounty), or if, in that case, it would consider the bounty failed altogether.