Vue reactivity doesn’t pick up new property added to element in a array

Not sure if I am explaining this right, but I am facing an issue where one of my template elements isn’t reacting to added property of an array element. For example:

Vue data updates in method with setInterval() but the dom/view doesn’t update

In my methods I have a function which is triggered using a @click in the view. This functions starts a timer, the timer works as I can see in the DevTools but it only updates in the DevTools when I …