I have two analytical friends who occasionally tell me when they confide in me or try that i am asking the wrong questions.

It is often an excuse to end the conversation but also sometimes said sincerely and with a lot of pent up frustration.

The thing is they started the conversations. So I’m confused. What are the right questions? Why don’t they just express what they want to or started to?
Why must I prompt them in a specific way? Is that normal? Am I failing as a good listener pr a friend? I always end up feeling upset that I let them down somehow. But I am also frustrated because I am not sure what I am doing wrong.

How can I fix this?