So i started a campaign using Reforged graphics and when I decided to use classic graphics either my save/progress vanishes or if they are there when i try to load them the game crashes.
is this a bug or once you start you have to stick to the graphic option you chose?
The Classic campaign and Reforged campaign are completely seperate. This is not a bug. The maps were all extensively updated, and some parts of the campaign are modified, in particular, the prologue missions added in the updated demo that was released after The Frozen Throne came out are added to the Reforged prologue campaign (thus the Reforged prologue has several additional missions), whereas the Classic campaign omits these missions. There is also significant differences in difficulty, particularly on Hard mode. Because of these differences, and because only Reforged campaign will unlock the new profile portraits, the campaign progress is seperate.
The one thing you can do about this is use the “All your base are belong to us” cheat to quickly clear missions to get your progress on one side to match up with your progress on the other. Note that the cheat codes do NOT block achievement completion. There are a few missions in the reforged campaign that are currently infamous for causing crashes. Save often, and if you find yourself unable to complete a mission because of this, you can use the all your base cheat to skip it.
aaah ok. Thanks. I was bit surprised by this issue but also in the Prologue I didnt remember going underground haha.
one small question, is Hard on Reforged harder than Classic graphics?
Yes. All three difficulties received extensive updates for RoC, and light updates for TFT. You will also notice remade missions, new units, and remade cutscenes.
You can read the change log here: https://www.hiveworkshop.com/threads/1-33-campaign-balance-update.340191/#post-3536510
ok.
but overall is it meant to be harder than the original?
Yes, Normal is a bit harder, and Hard is much closer to Brutal in SC2.
thanks 
i think i have my game plan set. woot woot
Fun fact: That’s because in the original Warcraft 3, this prologue was cut short. The island and the underground segments were part of a demo that was distributed ahead of release. With Frozen Throne adding custom campaign support, we got the full demo added in (With missing voices for some reason. Thankfully the restored version is available on Hive Workshop). Reforged took this and turned it into the standard.
Essentially, yes. Hard mode on reforged is considerably harder than Normal, and casual mode is considerably easier.
Something tells me that some of the cut content has battleships that had never been used in the main game unless if modified into it.
A few official melee maps had shipyard neutral structures, though they only had transport ships and not the battleships (which are in the data files). Not really related to the campaign or anything though.
I remember having that demo.
good times
I can imagine it would be in the campaign at some point. Since some of them had been used in a cutscene in where Mediev meeting with Jaina, Thrall and both Malfurion and Tyrande.