Its possible (2% chance) that your first encounter in the jungle is a CR 8 tyrannosaurus. You will very likely be level 1. So your TOA game could be "dicked over by NPC, town seems cool, TPK". It recommends that you are 1st-6th level for the hexcrawl portion of the game, and that you start at 1 leveling up 5 times as you crawl about.
They don't do anything like say "Not to imply the jungles near town are safe, but the further from town the characters get, the darker and more powerful the foes become. Use this second chart of hard encounters for this region". And then include the CR 8 stuff there. They also don't conveniently populate the low level hexes near town and the high levels ones far from it. I assume they assume your DM will cheat and not just TPK you with a T-rex during session 1, but you never know. If your players explore the bay right outside town, the module directly tells you that the dragon turtle shows up and wrecks their day unless they give him 50gp (a lot in level 1 5e terms).
When you end the game in the Tomb of the Nine Gods, you are expected to be level 9 or higher. If you kill the Atropal at the end, CR 13, Acerack himself shows up all pissed off, CR 23. Its not clear why you wouldn't kill the Atropal, it being a giant evil god fetus feeding off the souls of the thing you came here to break, that attacks you if you try to break the thing. you do get some buffs if you did some of the bullshit annoying puzzles earlier, but it turns it into an annoying grind. You get +50 temp HP every round, and +3d6 damage. you might be level 9 or 10, and he is CR 23, and you might not even have those buffs (the puzzles sucked a lot, so I wouldn't hold it against groups who said fuck it and ignored them). So you might just get fucked. It really comes off like a lot of the challenge from the module is just that sometimes stuff is way over CRed.
It really plays like they didn't actually run the game themselves. Just wrote the adventure, and assumed it was all good.