It's happened twice in my experimental Caves and Cliffs world, the first wandering trader spawned at Y level -41 and the second one spawned at Y level -22 in the span of ~7 in-game days, i see this being a problem for the people that actually care about them needing a conduit or maybe the brown dye before finding a jungle, they'd miss most of those spawns because of that small bug (taking on count how huge the caves are)