At the beginning of Avengers: Infinity War,
Hulk loses a fight against Thanos on the Asgard refugee ship. He is then sent to Earth by Heimdall, where he lands in the New York Sanctum and turns back into Bruce Banner.
Bruce Banner's first words after this are "Thanos is coming". This is surprising in itself as he was the Hulk until then, and in Thor: Ragnarok he described his latest transformation as being "locked in the trunk", i.e. not being aware of what happens at all (as opposed to his previous experiences).
Now you may recall that at the end of Ragnarok, Banner is still the Hulk. It's easy to assume that he didn't change back in the meantime, since
we could already see Thanos' ship during the mid-credits scene, and we never see Banner between these two scenes.
Yet Banner seems to remember what happened and to know quite a lot about Thanos, as he tells the team about his story and intentions.
Based only on what we saw, this is odd; it is not information he had beforehand and it doesn't seem like there was enough time for someone (e.g. Loki) to brief him about Thanos.
Has Banner been conscious during his transformation, or did he only turn into the Hulk in the first minutes of Infinity War - and learned about Thanos before that?