Some background, just because I think it might be interesting.
We've been running Storm King's Thunder with lots of homebrew and add-ons. My group began in Luskan as caravan guards on the way to Icewind Dale. I relocated Nightstone to the river you cross on the way north. Skipped the Tower of Zephryos. Tough and long journey to Bryn Shander through the mountains that included the Goldenfields attack re-imagined as an attack on the food stores of Hundlestone, which I have built as a stronghold of devout dwarves ruled by clerics of Moradin.
After various adventures in Icewind Dale, including the Forgotten Traditions and some other AL adventures set in a different northern snowy place, the party came into ownership of a huge fortune worth of scrimshaw (it had belonged to the merchant whose caravan they guarded who was eventually murdered and impersonated by an evil Luskan wizard). As well, they came to realize that the giants were looking for the Ring of Winter and so set out for Waterdeep.
They fought their way down to Luskan and travelled by ship to Waterdeep, where they could sell the scrimshaw and investigate Artus Cimber and the ring. I decided that this wouldn't be a red-herring in my campaign. Instead, they would be able to discover that Artus Cimber and the ring were likely in Chult and head down there.
I was planning on having them swiftly move on from Waterdeep and head to Chult, liberating material for that from Tomb of Annihilation. My players had different ideas. They spent a lot of time exploring Waterdeep, getting into trouble, buying things, and selling their Icewind Dale merchandise. Then they briefly dived into the well at the Yawning Portal.
In the Undermountain, one of the party--who had become an agent of the Zhentarim along with another party member, way back in Hundlestone--had his mind devoured by an intellect devourer. So now he secretly a double agent for the Xanathar Guild.
I decided that the two Zhentarim players would be sent to kidnap Raener Neverember, but with the description so vague that they couldn't tell the difference between he and his friend. So they wound up kidnapping both. The double agent informed the Xanathar Guild of these events.
When approached by Volo to rescue his friend, one of the Zhents immediately rushed off to get him from captivity (after all, he wasn't the objective and there was a reward). The other--the double agent--stayed back with the rest of the party at the Yawning Portal. The solo Zhent got to the warehouse, discovered the massacre, rescued Raener and followed the trail to the sewers. Injured and a bit worried, she returned to the Yawning Portal to get her friends.
But then the double agent attacked her when she made it clear she understood they were going to raid a Xanathar hideout. He took her down and executed her before the party eliminated him.
Anyway, that's where we are now. I'm trying to think about how to up the challenge level so that the party cannot breeze through the adventure.