I echo the above responses.
I think that the normal attention span is less than 30 min?
Add to that, extraneous stresses that you are worried about, and any conscious, subconscious, or unconscious memories that are being stimulated, in the situation. Closed room? With an authority figure? Similar sounds or scents that are present?
You might note the sensations, subject matter, and physical situation, and talk about it in therapy. Exercises like this have helped memories surface, that I could then process in therapy.
I always have found that is is helpful to pay attention to my body signals (including not being able to concentrate) and use that information to take some action to help me feel safer, or to help me concentrate better (e.g. take a bathroom break, state a boundary, change the subject, etc). Before I developed my voice and self-awareness, I used to feel almost 'pinned down' when someone would not stop talking.
You can also try making a plan, to help bring your attention back to the conversation (e.g. touching your wrist, etc.)