Bug: React 19 - Suspense Siblings Fall Back to Sequential Loading Under Load

[dkempner]

Originally posted in this issue.

The same code can execute sequentially or concurrently depending on the performance of the react application and the device.

In a challenging performance situation, Suspense siblings initialize as a waterfall instead of concurrently.

React version: 19.1.0

Steps To Reproduce

Source Code Links: Two Different Suspense-using libraries

• Using @tanstack/react-query: codesandbox.io
• Using @apollo/client: codesandbox.io

Repro Steps:

1. Open the app in a new tab (Example link for @tankstack/react-query)

2. Open network tools and refresh the page
3. Notice that the requests to dummyjson are made in parallel

4. Visit the performance tab in chrome devtools and apply 20x slowdown

5. Refresh the page
6. Notice that the requests to dummyjson are made in sequence

[dkempner]

I described the issue incorrectly. This is not a real bug.