That means you didn't practice enough listening to enable you to understand flluent conversations.
You better just keep practicing ,whether listening,speaking or reading,it all will help improve your listening skills.
You might at the moment be able to understand easy conversations, that you couldn't understand before,but not manage the more difficult fluent dialogues you hear.
Don't worry,because that means you are improving ,but you have to exert more effort to meet the requirements of a higher level of comprehension.
Good luck :)