How to debug inserting new DOM element with stimulus controller

I am inserting new DOM element as item of a list controller. This item is having a stimulus controller.
Previously, this was working fine, but today, these new inserted items are ignored by stimulus, the item’s controller is not attached and not initialized. But the same controller statically inserted in the DOM is working fine.

As I can not reproduce this bug in a simpler example, I am looking for a way to debug Stimulus, to find the issue by myself.
Or any known reason Stimulus is not watching DOM insertion.

Note I am using stimulus with Webpack Encore.

I also encounter that sometimes(also using Webpack). Have you tried reload-and-empty cache from the browser you’re using?