chrome addon VueJS element disappears when rendered

I have a successfully running developer mode addon that works in Chrome.

I would like a button on the page running Vue (which I’ve used for years). Here is my code:

    let isletCtl = document.createElement('div')
    isletCtl.id = "islet-ctl"
    isletCtl.innerText = 'isletCtl: '

    let isletVue = document.createElement('div')
    isletVue.id = 'islet-vue'
    isletVue.innerText = 'isletVue: {{ response }}'
    isletCtl.appendChild(isletVue)
    document.body.appendChild(isletCtl)

    window.setTimeout(function(){
        new Vue({
            el: "#islet-vue",
            data: function(){
                return {response: 'hello vue'}
            }
        })
    }, 25000)

The 25s delay was just to figure out what is going on. the button renders just fine, but when the Vue({ ... }) piece renders, the #islet-vue div just disappears from the DOM!

Anyone have an answer as to why this is happening?