What can go wrong in Mindfulness Therapy as used in Clinics?

I just stumbled across the article Mindfulness therapy comes at a high price for some, say experts . Even when mindfulness is practiced correctly, side effects may occur, like feeling lost or disconnected from the world. What could be the cause of the side effects? Do these techniques deviate a lot from the Suttas or orthodox practice? Do the staff have the necessary training and awareness required to give meditation advice (Kammaṭṭhāna )? Can something be wrong with how the clinic administers the training / teaching?