Invisalign attachments on bottom teeth slightly chipped in the middle, is it a cause for concern?

Hi, the attachments are placed on teeth mainly for either extra retention, to correct rotations or to extrude them. If it is only for extra retention, slight chip might not matter. I would still suggest to have it checked with your dentist if you don't know, what it was for for. The broken attachment could mean that the tooth won't follow the desired movement and thus will delay your treatment.