What are non connector elements?

I think I have a leak in my application because the rendering performance gets worse and worse as the user browses, while other sessions are unaffected and logging out, then back in, solves the problem.

I found the following lines in the Vaadin client log that may confirm my assumptions:

measured 5 non connector elements
measured 10 non connector elements
measured 15 non connector elements

The non connector elements set grows steadly over time, and there’s a straight line between a certain action and the number of non connectors leaked: for example processing a click on the “settings” button adds 5 to the count, while processing “profile” adds 6 and processing “home” adds none.

My question is what are non-connector elements and how can I identify them to understand where the leak is?