Yes, it can be a frustrating experience, especially when one knows there actually are things there that would be good to discuss but one can't access them.

I would start by talking more about what you have been talking about, just see if anything else comes up or if your T has any thoughts for you, etc. Just restate stuff you've said, but in a different way or wonder what your life might have been like if those things hadn't been part of your experience, etc.