Your customer may have implemented security policies that will block the loading of Heap (and typically any other client-side web analytics platforms). This can be because of policies blocking javascript from loading, which means Heap is unable to load and track events. This happens typically when Heap customers work with companies in more security-conscious industries like healthcare and financial services.
If you have mission-critical events you want to track, we encourage sending these in as server-side events, as Heap will still be able to capture these events for these customers.
To learn more about sever-side events, see Tracking Web Custom Events Client-side vs. Server-side.