Add to cart analytics event not registering when updating the cart right after

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We’ve had a merchant complain that since they installed our app their add to cart analytics have been inconsistent.
I have done some testing to try and figure out what could cause it and I found out that if you:

  1. Request to POST /{locale}/cart/add.js to add item to cart
  2. Right after the add to cart, you make a request to POST /{locale}/cart/update.js (we update cart attributes based on the new cart)

Then the event is not registered in the dashboard for some reason.
While if we don’t make the request to update.js right after the add to cart, then the event is registered correctly in the analytics dashboard. (edited)

I am able to reproduce this consistently.

I see the monorail events being sent correctly to the endpoint, but it still does not show up in the dashboard when following the 2 steps above.