Oftentimes the heap.push error occurs when Heap is unintentionally loaded twice on a site. For example, Heap might be loading once from the Heap snippet in your </head> tag (inserted during Web Installation) and also through a tag manager such as Google Tag Manager (GTM), Tealium, or Segment.
The error typically presents itself within the Developer Console when a Heap API call is made. In the example below, the heap.track call results in the heap.push error.
The fix for this error is to remove all extra instances of Heap and ensure it is only loading a single time on your site.