Describe the bug

When using markdown and lazy loading, sometimes messages are rendered twice or they are not even rendered.

Expected behavior

Messages should render without the mentioned issues with these two features

Minimal reproducible example

It is reproducible in the markdown demo. Just add some long markdown messages (a lot) and start scrolling

Add-on Version

latest stable

Vaadin Version

latest stable

Additional information

This problem seems to be related to using virtual-list. Consider using a minimal grid instead.