It's clear to me that D&D created the NK because they thought the show watchers would need some tangible enemy to be the big bad instead of just a general menace of zombie like characters behind a wall.
I'm ok with that as choice but don't build up all this intrigue and mystery around the character if you gonna just ignore it when the character's arc comes to an end.
I didn't miss it. This is only the latest Winter. There was a winter that lasted for 3 years or something like that during Neds lifetime. I remember reading Tyrion was born during the same Winter. So Why was this winter special?
Remember the first scene of season 1 was The White Walker killing Wildlings and men of the Nights Watch. No one had seen them for a 1000 years and this was before Bran got crippled and before Danys dragons hatched.
So what triggered the Walkers and NK to come south?
The only thing that makes sense is thst Jon's birth fulfilled some prophesy that triggered something with the Walkers but the show makes it Clear that Jon was not the focus or worry of the NK.
Assist.
You may have forgotten about this scene from season 1 that might answer some of your questions...
OSHA told Maester Luwin that the White Walkers had been sleeping (ie hibernating) for thousands of years... ‘but they ain’t sleeping no more’.
So if the Walkers were indeed hibernating all that time... there would have been
‘no opportunity’ to (intentionally) attack the South before now.
Also, it was never said that the Night King actually HAS greenseer sight, on the tv show.
Personally, I don’t think that the Night King ‘knew in advance’ that he was going to get a Dragon one day

... or had even ‘planned out’ his attack to take place at this specific time. (Keywords: specific time’)
But I DO think he knew he could not get past the Wall... and he just ‘seized the opportunity’ to kill a Dragon & use it to ‘break free’ from the embedded Magic that was stopping him from going beyond the Wall.
The dude is already dead. So his perception of time is probably completely different than ours.

Or the concept of ‘time’ itself might not even exist at all for him

... the way it does for us regular humans.
He could’ve hibernated (or just closed his eyes) for only 10 minutes by HIS watch... then woke up and said to himself: “Ok, this power-nap is over. Time to kill everyone in sight for taking my humanity away from me.”

(Meanwhile, thousands of years & multiple ‘seasons’ had passed on every Westerosi Calendar.

)
So to me, it just seems that he can just ‘detect’ Bran’s (or a 3-eyed Raven’s) presence whenever he is directly INVOLVED in their thoughts / or dreams.
Which means no matter ‘where’ Bran is... the Night King will ‘detect his presence’ if Bran is ‘visiting him’ - regardless of he is dreaming, or wide awake.
But he doesn’t actually ‘see’ all the same events / or memories that Bran sees.
For example: Bran visited the Children of the Forest when they created the Night King... so the Night King can establish ‘a connection’ to Bran (or detect his presence) in that specific dreamlike state.... because he is specifically INVOLVED in that scenario.
Bran also visited the Army of the Dead, right outside the 3-eyed Raven’s Tree (North of the Wall)... so the Night King can establish ‘a connection’ to Bran (or detect his presence

) in that specific dreamlike state.... because he is specifically INVOLVED in that scenario.
But when Bran went back and saw Ned as a youngster practicing swordplay with Uncle Benjen at Winterfell... or when Bran saw Ned fight Sir Arthur Dayne... or when Bran visited the Tower of Joy to learn about Jon’s true parentage... or when Bran saw the Marriage of Lyanna Stark & Rhaegar Targaryen... the Night King doesn’t appear, nor does he detect his presence, in those specific dreamlike states... because he is NOT INVOLVED in those scenarios.
It’s like... the Night King is always real... and he can always touch / interact with Bran... whenever Bran is just thinking about him (or an event that INVOLVES him)... even if Bran is (literally) sleeping, or warging or doing something else, hundreds of miles away.
I don’t have an in-depth explanation of ‘how it works’... I just chalked it up to the same type of (Supernatural) “Black Magic” that allowed Melisandre to give birth to a Shadow Demon... or allowed a flame to ‘speak’ to the Sorcerer who mutilated Varys.
It’s just ‘black magic’ stuff & they established that there’s lots of different types of it on the show. And that’s good enough for me.
