Date Encountered: July 14th, 2019
NPC: Qeshi-Rae, The Crystarium (11, 8)

After accepting the level 78 delivery for Qeshi-Rae, gather and deliver 18 Megafauna Traces to her. In the cutscene that follows, Qeshi-Rae says:
This worries me, [player name]. What if this proves the be the last surviving creature?
I believe this is definitely intended to be 'to be the'.

I will attach below a screenshot of the text in question:
https://i.imgur.com/6nF7FzX.png