Why did the quality of Harry's visions of Voldemort go down?

Question

It makes sense to me that the visions Harry sees into Voldemort's mind don't happen all the time. In year five he sees into Voldemort's subconscious pretty often. In year six Voldemort starts using Occlumency to shut him out. In year seven the visions start up again. What doesn't make sense to me is the changes in the quality of the visions that start half-way through The Deathly Hallows.

The only other thing that mattered to him was that his scar had begun to prickle again, although he did all he could to hide this fact from the other two. He sought solitude whenever it happened, but was disappointed by what he saw. The visions he and Voldemort were sharing had changed in quality; they had become blurred, shifting as though they were moving in and out of focus. Harry was just able to make out the indistinct features of an object that looked like a skull, and something like a mountain that was more shadow than substance. Used to images sharp as reality, Harry was disconcerted by the change. He was worried that the connection between himself and Voldemort had been damaged, a connection that he both feared and, whatever he had told Hermione, prized. Somehow Harry connected these unsatisfying, vague images with the destruction of his wand, as if it was the blackthorn wand’s fault that he could no longer see into Voldemort’s mind as well as before.
_{(Deathly Hallows, Chapter 22, The Deathly Hallows).}

I find it hard to believe that the changes were because of the wand since he sees into Voldemort's mind perfectly clearly later in the book when his wand is still snapped.

Is it because the connection between him and Voldemort is weakening? That's certainly not what other parts of the books suggest. Dumbledore seems to contradict it as an idea:

“Meanwhile, the connection between them grows ever stronger, a parasitic growth."
_{(Deathly Hallows, Chapter 33, The Prince's Tale).}

I'd also rule out the idea that Voldemort was using Occlumency since he didn't seem to be doing that at all during the events of Deathly Hallows.

Has it ever been explained what the cause of the disruption in the clarity of the visions was? Is there an in-universe explanation?

Answer 1

It's complicated.

As you point out using the excellent quote in Why did Voldemort stop employing Occlumency against Harry in Deathly Hallows?, Voldemort stopped using Occlumency in the Deathly Hallows. He stopped using it,though, a year earlier in the Half-Blood Prince.

In the Half-Blood Prince, Voldemort does a very good job with the Occlumency. However, for the first time in a year, his concentration slips in The Seven Potters. Harry's scar burns when Voldemort finds out which is the real Potter (a moment of intense euphoria) and when Harry, yet again, slips through his grasp (a moment of intense anger.) Then, Harry is sent this vision:

“You told me the problem would be solved by using another’s wand!”

And into his mind burst the vision of an emaciated old man lying in rags upon a stone floor, screaming, a horrible, drawn-out scream, a scream of unendurable agony. . . .

“No! No! I beg you, I beg you. . . .”

This kind of extreme emotion did not happen in book 6, except maybe when Dumbledore was killed, but Harry would neither have noticed or cared then. In addition, Voldemort is intent on what he's doing--flying around trying to kill Harry Potter--and can't focus on Occlumency.

The other visions he has--times when Voldemort's Occlumency slipped--are all moments of intense feelings, like when he finds out that Harry has the Cup, or when he gets the Elder Wand. In addition, Voldemort is doing a lot more than he did in book 6--things such as run the Ministry. You've got to imagine the guy is stressed; who cares if his Occlumency slips once in a while.

But now we get to the meat of the answer. Why is the quality different? It has nothing to do with the connection, it is because Voldemort was trying to supress the connection. While in earlier books he didn't know/care about the visions, now he is trying to suppress them, however the connection is simply too strong. It's getting stronger, and sometimes Voldy forgets, or loses control, as this excellent answer states.

Answer 2

The Dark Lord’s Occlumency had partial effect.

Harry’s blurry visions into the Dark Lord’s mind were likely a result of the Dark Lord’s Occlumency being partially successful - working well enough to block Harry out somewhat, making what he sees blurred and not as clear, but not blocking him out completely. The Dark Lord began using Occlumency to keep Harry out of his mind when he realized the access that Harry had to his thoughts and feelings. When he was most successful at using it, he was able to completely shut his mind, and Harry didn’t see into his mind at all.

“So tell me, Harry,’ said Dumbledore. ‘Your scar … has it been hurting at all?’

Harry raised a hand unconsciously to his forehead and rubbed the lightning-shaped mark. ‘No,’ he said, ‘and I’ve been wondering about that. I thought it would be burning all the time now Voldemort’s getting so powerful again.’

He glanced up at Dumbledore and saw that he was wearing a satisfied expression.

‘I, on the other hand, thought otherwise,’ said Dumbledore. ‘Lord Voldemort has finally realised the dangerous access to his thoughts and feelings you have been enjoying. It appears that he is now employing Occlumency against you.”
_{^{- Harry Potter and the Half-Blood Prince, Chapter 4 (Horace Slughorn)}}

Once he started, the Dark Lord keeps trying to use Occlumency to keep Harry from seeing into his mind, with varying levels of success. As J.K. Rowling states in an interview, he was losing control and was sometimes unable to prevent Harry from seeing into his mind.

Maura: How come voldemort was no longer employing occlumency against harry, as he was in the 6th book

J.K. Rowling: He is losing control, and unable to prevent Harry seeing into his mind. The connection between them is never fully understood by Voldemort, who does not know that Harry is a Horcrux.
_{^{- Bloomsbury Live Chat (July 30, 2007)}}

At times, the Dark Lord’s attempts at Occlumency failed completely, and Harry sees into his mind as clear as ever. When Harry sees into the Dark Lord’s mind, but it’s blurry, this likely means the Dark Lord’s Occlumency against Harry was partially successful. It was keeping Harry out enough where he couldn’t see into the Dark Lord’s mind clearly, but it had slipped to the point where Harry could still see into his mind somewhat.