Where are the infestations???

I’ve spent hours in a world and world hopping and haven’t seen one appear more than once for less than a minute? Are they deactivated? Is it luck? Is there something I have to do to make them appear? I haven’t been able to get my infestation challenges done at all, and I am trying to interact with the system to give feedback but they just aren’t happening! If anyone can give advice/help I’d really appreciate it!