What went so absurdly wrong that the Gnolls got close enough to deal damage in melee?
In the first encounter on the road with the hyenas, kill the hyenas from range, walk around the hill and circle back toward them from the higher elevation, keep going past them to the ledge that hooks back around. Two rounds, max, you should be able to take them out with long bows and short bows. They should never even get close enough to see you. Sneak attack helps here, but other that that, I used arrows and cantrips (I refuse to let my party sleep since Lez wants the cure first). If you are talking about the second, sneak up to the top of the overlook near the cavern entrance. Kill the unit closest to you with stealth (Rapier, 16 dex, it was a one hit kill and should always be an automatic crit) which launches a surprise round in which you should be able to pick off the caster and one or two of the damaged archers. The Flind and the hyenas shouldn't do anything for two more rounds. By that time, only the Flind should be left. If the Flind is left at all.
.
This is all just free xp
And this is why the game is essentially broken as is, because the encounters are not designed with 5e balance in mind but they are designed such that ranged combat is so superior that making a melee character is gimping your party. Monks will be all but useless as it stands now, because some of the nastier encounters can be soloed at range using the broken stealth system, but trying to use melee in the same encounter is essentially suicide.
Challenge rating in 5e actually means something to the balance of the game. A single ogre has a challenge rating of 2, meaning it is a solid risk-reward encounter for a group of 4 second level characters, 3 ogres is coming up CR 7 on the encounter calculator I found - you can't even have level 7 characters in the game yet. Standard 5e gnolls are CR:1/2 but these gnolls are way beyond that with the multi-attacks they get, actually only pack lords and fangs of yeenoghu have multi-attack, pack lords get 2 and fangs get 3.
Point being if you use ranged, altitude, surfaces, and the broken stealth system you can cheese these combats, but outside of that you are going to get torn apart which is why you have so many people complaining about the difficulty.
