I also had the "no trader" show up after completing the starter quests, although i did not have disappearing pois.
My son teleported to all the traders, and the problem was that we had no forest biome traders spawn. Traders in the desert, the snow, and the wasteland.... but no forest. If i remember correctly, the initial quest to go to the trader always sends you to a forest trader, so my assumption is that that is the reason we got "no trader".
It was a crappy map anyways, so we generated a new one. The new one had forest traders and the quest worked as expected.