For very large pivot tables (> 5000 total cells) there is a noticeable lag between when an action is kicked off and when the spinner shows up to signal that something is happening. Two points for us in particular:
1. When first loading the pivot table, it shows a blank screen while processing the data before the spinner shows up
2. When sorting or expand/collapsing, there is a lag between clicking and the spinner showing up
The reason I believe this is happening is that in PivotView (@syncfusion/ej2-pivotview/src/pivotview/base/pivotview.js), the prototype methods that call showSpinner (for example onDrill) often also kick off a lot of processing for large pivots. It seems like that data processing prevents the render from happening that would show the spinner. I was able to get the spinner to show up right away by calling showSpinner and then placing the rest of the method in a setTimeout with 0 seconds so that the data processing is kicked off on the next cycle.
Here are videos of the issue and the fixed behavior: