Hmm, I took a listen and Wanderer plays twice as often as any other exploration track. Like in the original game, you can change the exploration track by either waiting for the current track to finish, or by switching to the map, then back to exploration. If that's not working for you, could you check for UW04.xmi in your original game installation folder inside SOUND?
Been testing and it sounds like it's maybe two different version of the same track (I have the UW04.xmi in my SOUND folder), or maybe it cuts off? I'm using Ultima Underworld Portable (Roland MT-32) for the original, which sounds exactly like the one in the linked video. In the Unity version it never seems to reach the crescendo, as here at the timestamp (1.38), and it sounds differently throughout: