Why is the link to the html node not working?

Question

JavaScript

The problem is, I create an html node using document.createElement and assign it to a variable. After I change the html in the code using this variable, it often works, and sometimes it doesn't work. It seems that there is a value in the variable, if you add a class, for example, in the variable it appears in the classList, but nothing happens in the html. It turns out that there is a link to the node, but it is no longer relevant. Why is this happening?
Interactions with dom occur in this way https://codesandbox.io/s/suspicious-tesla-2rl4h?fi... , this code is working, but within the program it may stop behaving correctly, that is, manipulations using this.$ root where the node is stored don't produce any results.