From the addon description:

WARNING* This addon is NOT compatible with the story mode, it won't crash the game or anything but will turn some factions hostile. If you want to buy spells in the main story you can *Disable* this mod -in game- ("Main menu" > "addons") and install my addon below!

EDIT* The Npc AkaviriBlade was added to prevent players from making it too far in to the storymode just to encounter a hostile faction preventing you from completing the game! There is no reason what so ever why you would even want to play the storymode with this addon... If you want to buy spells in storymode then disable this addon and download my other addon "Spell Merchants"...

I would love to merge these two mods, the only reason they are separate in the first place is because they are incompatible. You see, in order to get friendly npcs (who can talk) to spawn in ID I had to manually disable some code then (manually) turn all factions hostile (so the levels wouldn't be filled with friendly wizards and other npcs standing around all derp like) you can see the chaos this would cause if you try playing spell merchants with ID Merch active... Some towns would go ape s**t and attack you on sight. So sorry, but they cant merge... well... they could, but I dont even want to deal with that head ache again (involves using stores to sell the spells) and the amount of hours wasted trying to get that to work, I'm afraid only Dark God him self could pull that off.

I just had a merchant generated with a summoning alarm (and was mildly amused at his "hmmm?" response to suddenly appearing in a dungeon surrounded by multihued drakes and hatchlings.) He was the steamtech merchant, but was just called "Sun Paladin" and would spontaneously engage me in dialogue if I stood adjacent to him. It took 2-3 tries to say goodbye, i.e. when I told him I just wanted to go, the dialogue box would immediately pop up again, and occasionally for a third time before it stopped. It was just a minor annoyance, but given that it didn't always take the same number of tries to disengage from conversation, and that he forced me into conversation without my say-so, it did occur to me that there's a possibility of getting stuck in the conversation indefinitely, necessitating an emergency shutdown and restart. That might not necessarily be a danger, depending on what mechanism is preventing me from leaving the conversation the first time I try, but I figure it's an issue worth sending your way. If it matters, this particular character started out back during your previous versions, before there were independent NPCs doing the selling rather than storekeepers.

He looked like an orc (necromancer), to be clear. He was just identified as a Sun Paladin with no name.

That's a feature, not a bug. It's part of the main campaign. You play undead, you have to deal with the annoyance of remembering to switch in your Cloak of Deception before dealing with towns, shops, and civilians.

If you're playing the main campaign, you'll quickly learn that adventurer parties on the world map? Not people you want to piss off by looking, well, dead. Once you've met a few, you're likely to remember to put on that cloak every time you leave a dungeon.

My guess is that if you're level 60, you started this character before dropping the add-on into the folder. Without futzing around with non-gameplay stuff (and, no, I can't tell you how to do it, just that it's possible) the add-on won't be active with this character. You'll have to start a new one with the add-on enabled from the start.

But the ID has some seriously OOD monsters. I just met (well, saw via tracking and fled like hell) Urkis on level 2. On Normal difficulty, mind you. Luckily, he was too busy pondering whatever it is insane tempests ponder to hear me screaming and knocking stuff over as I ran away. I've seen leaders of the Orc Prides in the first five levels before. Handling the ID requires a slightly more paranoid approach than the main campaign because, well, you *will* meet the killer of your dreams eventually, and probably sooner rather than later. Explore carefully and stock up on emergency escape options. Best just to think of ID as a decidedly different game than the main campaign and create entirely new strategies for surviving it.