Bottlenecks are the tasks which slows you down. Development teams work on smaller task to achieve a goal. If the task is stopped in a particular stage due to any reasons such as waiting for the other task to complete or waiting for any specific requirement to be verified, then they become a bottleneck for the entire process of development. A product manager should identify these bottlenecks and sort them out as soon as they can.
We know this is a difficult tasks and this is one of the driving factors we are building an idea management system in MyProductHub. This will allow you to collaborate with your team and sort out there issues before the idea reaches the development cycle.