Runtime error: "Element type is invalid" for React 19.2 Activities

[AdrianAndersen]

Link to the code that reproduces this issue

https://github.com/AdrianAndersen/next-react-activity-bug

To Reproduce

The provided repository is created using pdx create-next-app@latest with defaults.

I then upgraded to react and react-dom 19.2.0 and added an Activity

A runtime error is thrown when you visit http://localhost:3000/ in dev mode, or when you try to run a production build.

Current vs. Expected behavior

A runtime error is thrown when a React Activity is present in the rendered code

Error Type

Runtime Error

Error Message

Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. You likely forgot to export your component from the file it's defined in, or you might have mixed up default and named imports.

Check the render method of Home.

Next.js version: 15.5.4 (Turbopack)

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 25.0.0: Mon Aug 25 21:17:51 PDT 2025; root:xnu-12377.1.9~3/RELEASE_ARM64_T6000
  Available memory (MB): 16384
  Available CPU cores: 8
Binaries:
  Node: 22.13.1
  npm: 10.9.2
  Yarn: 1.22.22
  pnpm: 10.16.0
Relevant Packages:
  next: 15.5.4 // Latest available version is detected (15.5.4).
  eslint-config-next: N/A
  react: 19.2.0
  react-dom: 19.2.0
  typescript: 5.9.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

React

Which stage(s) are affected? (Select all that apply)

next build (local)

Additional context

I also tested on 15.6.0-canary.41 (as of writing the latest canary), and the error is present there too.

I tested React Activities in a TanStack Router project, and since it worked there I assume this is related to something in Next.js. Please correct me if this should be submitted somewhere else.

[icyJoseph]

Duplicate, #84462 - I think, right?

[AdrianAndersen]

Ah yes, didn't see that one. Feel free to do whatever with this issue. Based on that thread I assume that this will be resolved in the next version of Next.js.

[AdrianAndersen]

BTW @icyJoseph
You said that:

AFAIK, both Activity and useEffectEvent stable should be available in next@canary already.

I tested just now, and it does not seem to work on 15.6.0-canary.41

[icyJoseph]

Interesting, but useEffectEvent does right? I guess one more sync is needed 🤔 but it is the same issue. Do you mind closing the issue? I imagine many will try this out over the weekend, we should centralize into one issue.

[AdrianAndersen]

useEffectEvent works on 15.6.0-canary.41, <Activity></Activity> does not.

Feel free to close this issue, might be a good idea to update the title of the other one so it covers both cases and is discoverable for the people 👍🏻

[denk0403]

I tested just now, and it does not seem to work on 15.6.0-canary.41

React 19.2 accidentally excluded Activity from usage in server components. This is fixed in React canary, so it will likely be fixed as part of the next Next canary release. You should be able to use Activity in client components in the meantime.

[marvinscheffold]

I´m running react 19.2.0 and get the same error inside a client component