They should not just suddenly appear perhaps the linkage to the event is wrong. Originally they were not under the control of the player (AI or human) at all and would suddenly appear in cities with unhappiness or unhealthiness but there should have been a message.
Someone has changed the iCost value in the XML for the band it used to be -1 meaning you can't build it now it is 5 which means you can. I am assuming that someone decided that you should be able to build the. It dpoes not seem right to me as you will now be able to build cities before tribalism.
Edit the cost of a settler is zero



. A colonist still costs 350 - I Think we may have someones test costs in here.