I have been using ant bait for a while now. The ants usually eat the bait and then disappear, but then they pop up in a different room. Why is the bait not working?

Ant bait is meant to be one part of the control process. Bait alone will not wipe out an entire colony, and using bait alone will take a very long time to get you the results you want. Ants are also very good at adapting to their environment. They can determine if a food source or food location is killing them. Once they catch on, they stop feeding from that location, or from that bait entirely.