I've had serious issues with the sleep poison as well. First of all, it's worse than you think, the text says (page 67-68 and repeated on page 75) "A casting of dispel magic using a spell slot of 7th level or higher can also end the effect".
Now the first time I read this, I assumed that they intended the poison to be impossible to remove, since it says "if magic is used to cure the poisoned condition, the recipient becomes immune to the poison's effect for 1 hour"; ie, you're still poisoned, you're just temporarily immune. I still think that interpretation makes the most sense, but my players (and Sage Advice) pointed out that since dispel magic can 'also' end the effect, the English language prevents that from being the only way to remove the poison.
One of my friends thought that the dispel magic was what you'd need to dispel the cloud of poison gas, as opposed to removing the poison- and while that also made some kind of weird sense, that interpretation was debunked by the sleep poison you encounter on page 75.
Sage Advice has yet to comment on the dispel magic- if it was a typo that missed the editing process that's one thing, but it's printed this way twice (so someone made this ruling and then copy+pasted it). The original adventure doesn't say word one about Dispel Magic, so this is part of the conversion.
Why there is an "option" to remove a magical poison that is basically impossible for players to employ is ridiculous. Now granted, Hidden Shrine is an old-school adventure, and those were notorious for having cool magical things cast at stupidly high levels of casting ability so they would be "tamper proof". And the Shrine has lots of stuff like that, for example, the Glyph of Warding + Bestow Curse combo on page 68. Which not only requires a stupidly high level spell slot for a Tier 2 adventure, but also does something neither of those spells can do, ie, hit multiple targets with Bestow Curse.
But this is just mind-boggling. By the rules of Dispel Magic, what the text should say is that the DC to remove the poison is 17 with a caster ability check, and you'd need a level 7 Dispel to not require the roll in the first place. That's not what they wrote down.
All in all, this was a terrible conversion. There are traps with no DC's to notice or disarm in various parts of the dungeon as well, which annoyed me so much when I noticed them, that I just told the party "you find the trap and remove it because apparently, the DC is either 0 or 50." Really the DC's should be 15 or 20, like most other things in the Shrine (not counting all the areas lightly obscured by poison gas which would give disadvantage on Perception to the players and lower their passives by 5).
If you want to run these adventures, I suggest you get pdf's of their original versions and convert them yourself. 50 bucks for a book with as many issues as it has is ridiculous.
One out of Five +1 Daggers.
