I guess it is most likely a flash issue.
Minor bugs: Scalder came back with about 400 mana and Yue Fang just with about 100 mana when they got revived in Yellow Turban Rebellion.
Also, this level isn't such hard, but for that there is a very bad missing infocard mistake in it. There is absolutly no information that you can upgrade your troops at the alter. Maybe also add a hint that it is easier to get the bonus supplies if you attack the base from behind (since otherwise yuo will encounter reinforcements from the base which will follow you -> much more enemies then)
Book 4 Chaper 1 mission doesn't fail if Sorona dies. Not sure about Nekurow's death. €: Ok, it seems that it only fails if both heroes are killed, different form the quest description.
This chapter could also need some balance reworking. For instance, sometimes the undead forces attacks you from behind while you are fighting another group of enemies. I even have the feeling that the undead forces (at least the group with the lich) has a fable to go where the player is instead of attacking the NPC bases. €: Yep, they are persuethe player definitivly.
Also, the waygate quest seems to be too hard since the acos are setting it up too fast.
Reduce also a bit the units of each group since it is even hard to stand one group with your two heroes. Reduce the damage of the Eclipse Cannon a bit.
Also, during the whole campaign a big problem came over me over and over. For quests there are those pointers, you know, those small green circles at the navmap. Well, they do disappear far too fast, very after I had towonder where I have to go to. Very often those pointers came during a dialouge, and of course I was still reading it. So, two suggestions: Make the pointers longer appear. PLUS: Let them renew every then and then, so even if you forget where they are you can see them later again.
Nekurow doesn't has the chaos attack type in book 4, chapter one (dunno about the other chapters since I am still at that one)
Some part of the history descriptions of some orbs are missing (took a look at RazorClaw X hero ingame in book 4 chapter 1)
The cooldown time for Disruption Web seems to be too long for me
Orpheus' Journey: It somehow Charm seems to be bugged...some units of me (at least one, it was a Cold Wraith) didn't totally obeyed my orders, i sent it to the fountain of health but it always went to a other location after some time (yep, i removed it from group/selection and even gave him the Hold Position order, buit nothing changed)
I have the feeling they return to the location where I charm them from. I guess they somehow still get orders from their former owner. (Not directly of course, but the map gives them orders I mean)
€: This seems to happen to all charmed undead units, at least it did to my spiders as well.
Book 3, mission 1: The murloc's don't really obey the player's order even if the raiding party got taken out. I mean, you can get them into your group and can order them things, but the order will get overwritten by the NPC's ones over and over. So an unit, for instance, which you sent to the hidden entrance of the enemy base might attack at the front door since the NPC started an assault with it's units there.
You should also rework a pretty minor thing with the Corona race. At least the archers (maybe even a few other units, those casters with web maybe?) don't have automatically enabled autocast for their arrows when they come out of the boneyard.
Book 4, chapter 4 (?, that level where you start with Abolisher): seems to be also very hard, not only cause of the summoned hell beasts (but also), you will get attacked very early (I set up like 7 towers or so), Shizuka's party comes in too late (IMHO) plus they dont give you SUCH an advantage that you could beat the hell beasts easily, plus the normal dude first has to check their spells since they don't know them (remember, you just changed their classes a chapter before)
Another thing which has annoyed me during the whole campaign are the incorrect priorities in the selection for heroes. For instance, in the normal WC3 your first hero has always the first slot in the selection, the second hero the second slot and so on.
Chapter 4
Black Moon Orb. Restore power to all ten Obelisks and Abolisher will start out with the Orb of Death.
10 (?) Obelisks? Where is the last one then? In the class selection interlude it was stated to me that all 9 (!) Obelisks got activated. Plus, aren't there any murlocs at the easy difficulty in that level? I fail to see their base....