Wandering traders ALWAYS spawn at the lowest spawn point possible. If there is a cave underneath the surface where they were going to spawn, they will spawn there.

Under my village, around -50 up to 32 there are major caves and a mineshaft. The wandering trader ALWAYS spawns somewhere down there, never on the surface.

Even without a village nearby, if they spawn, it will happen. I seldom find the wandering trader on the surface at all, but when I am working on caves I will occasionally bump into them.

Pretty sure this is a bug, I believe they should spawn at the closest possible point to surface (64 Y) and not the lowest point. Happens in both local and multiplayer.