Mainly their lack of a clear communication and action on the topic discussed in this thread.
And also (until their recent rollout of a new web interface), the previous web interface was very slow and clunky.
And that a “normal” 2FA took years to implement.
That said, I’m sticking with them, for now. Maybe “rapidly increasing frustration” was an exaggeration. Better would have been “moderately growing annoyance”.