The second line repeats the first almost word for word and moves the injury up one level. Legge's translation shows the couch overthrown by injury to its frame, again says the injury goes on to destroy all firm correctness, and again gives the verdict of evil. The repetition is the point. Nothing has changed except the height of the damage, which is what a decline actually looks like from inside it: the same thing happening again, slightly higher up, while the response stays the same.
Frame is a more serious loss than legs. Legs hold a couch off the ground; a frame is the couch. Once the damage has reached this level the article is no longer merely unsafe to stand on, it is beginning to stop being what it was. The hexagram is patient about this, spending two full lines on the ascent, and that patience is itself a description of how such processes are experienced rather than a slackness in the text.
A yielding stroke correctly fills this even position and holds the centre of the lower trigram Kun, so by the ordinary measures this is a well placed line. The verdict of evil arrives anyway, which is the harder teaching in it. Correct conduct in a correct position does not stop a decline that nothing firm is opposing, and the absence of any strong line in the whole lower half of the hexagram is why personal soundness here is not sufficient to arrest anything.