Would have been better if you mentioned it was with UMSWE because it editor crashes when it loads a UMSWE map.
After browsing through your map with MPQ viewer, I was able to get a clue which is the structure in question. Really, there are hundreds of raxes with overlapping unit assortments. Guess that's also the reason why it does not bug for most other buildings.
But yeah, it seems you have not understood me. The ability is added/removed in a couple of triggers, in set the units variables for example before a Burning Legion Base comes into play. Seeing that you have more than one building with this ability and that trains units, even if you had only the above trigger, it would run once to place a Stormwind Town maybe, add the ability, on another run create a Burning Legion Base, so the trainable units that Burning Legion Base offers and that were not used before, all get initialized after the ability was accessed for the first time. I would advise you to initialize all trainable units on map init before the ability (throw all of them in an array or the structures that possess them, then loop over this array and check their classification for example, what you do does not matter, essential is that somehow the game is instructed to read the units' object data).