Someone had already pointed this bug not long before. The fix is quite simple:
1.Open the World Editor through "Launch Editor" option in Blizzard App.
2.Press F7 (this will open up the Campaign Editor).
3.File -> Open Campaign -> choose "05_NightElfX_1.33.0.w3n".
4.Navigate to "Custom Data".
5.Edit -> Reset Standard Units to Defaults -> Yes.
6.Save changes.
You have to repeat this step for both Human TFT and Rexxar campaigns. And remember, your campaign progression will be reset with this edited one.
Source:
1.33 Campaign Preservation Project