In our last play session in Chult, the party faced a number of pterafolk, who used their Terror Dive on us:
If the pterafolk is flying and dives at least 30 feet straight toward a target, and then hits that target with a melee weapon attack, the target is frightened until the end of its next turn.
It wasn't clear whether "its next turn" meant the next turn of the pterafolk or the next turn of the target.
At the time, it was suggested that "its" referred to the target because that was closer in the sentence to "its". That 'felt right', but none of us are grammarians. My research since then seems to indicate that proximity is not a rule for ambiguous antecedents, and it is difficult to find interpretive guides because most of my Google results just return style advice that say "Don't write like that" rather than 'this is how you should interpret this'.
In terms of how the frightened condition works in D&D I haven't found any consistent principle, since, for example, the frightened condition caused by a fear spell or a Demilich's Howl ends on the turn of the target, while the fright caused by my Battlemaster's Menacing Attack ends at the end of the Battlemaster's next turn, not the target's.
Is there any guidance on how to interpret on whose turn the frightened condition ends?