Janina Fisher explains this really well too, I went to a work shop of hers and it was pretty much about trauma and how these particular clients fear intimacy but also crave it so working with a therapist can provoke lots of anxiety.
She also says that our memories are stored in our bodies so if we have insecure attachment we will be very sensitive to any form of abandonment by the therapist. We are constantly looking fr signs or signals from them, we have learned that people aren't safe and we cant trust them.