My game has spawned multiple Wandering Traders simultaneously, which according to snapshot 19w05a ought to be impossible (it's stated that only one exists per world). One spawned near a village I had been building on my Survival world (comprised of only two villagers at the time) and another spawned near my house (roughly 80-100 blocks from the village site) one in-game day later. I've included a screenshot of the two traders together at the built village, as well as what I believe to be the logs from the play session (the logs may be rather long, but I exited the session shortly after this happened so any relevant data ought to be close to the end of the logs).