Hello,
If the preview UI tries to display a data structure with a circular structure it fails at JSON encoding, an uncaught exception gets thrown and the UI doesn't update.

This can happen for example in the following setting:

• define an AllElementsClick trigger
• open the tracked website in debug / preview mode
• give an element on the page a reference to itself, e.g. el.selfref = el;
• click that element
• mtm.clickElement will be pushed to the datalayer
• And here is what I assume is happening: the preview UI tries to JSON encode the datalayer to display it and fails due to the circular structure caused by the self reference.

Of course the given example is a bit silly, however for example when a UI framework that binds a circular structure to the element is used this becomes an issue.
For instance, vue binds a __vue__ property to the root element of a component from which a circular structure is given via __vue__.$el.