No gate: the picture moves and unprepared layers are absent from it.
Playback waits to begin, and stops again at any frame whose artifacts are missing, until they arrive or the gate's own wait bound gives up on them.
Playback waits to begin; frames after that are not held.
What a playback gate holds back.
A source the renderer pulls samples from can be held between any two frames, because the renderer decides when each one is drawn. A source that presents its own frames owns the playhead, so holding it means stopping the producer and starting it again, which the detection gate does and the render-preparation gate does not.