ng serve warning: Angular detected an incompatible configuration, which causes duplicate serialization of the server-side application state. #63524
Description
Which @angular/* package(s) are the source of the bug?
platform-server
Is this a regression?
Yes
Description
I occassionally see this warning in the terminal when running ng serve (Angular 20.1.x and latest 20.2.0).
The warning doesn't seem to cause harm but the source of the issue is not very clear, since we don't have ServerModule anywhere in the code, and our app.config.server.ts is the standard/simple:
import { ApplicationConfig, mergeApplicationConfig } from '@angular/core';
import { provideServerRendering } from '@angular/ssr';
import { appConfig } from 'app/app.config';
const serverConfig: ApplicationConfig = {
providers: [
provideServerRendering()
]
};
export const config = mergeApplicationConfig(appConfig, serverConfig);Could you please provide additional clarification / tips for resolving this warning?
Please provide a link to a minimal reproduction of the bug
No response
Please provide the exception or error you saw
Angular detected an incompatible configuration, which causes duplicate serialization of the server-side application state.
This can happen if the server providers have been provided more than once using different mechanisms. For example:
imports: [ServerModule], // Registers server providers
providers: [provideServerRendering()] // Also registers server providers
To fix this, ensure that the `provideServerRendering()` function is the only provider used and remove the other(s).
Please provide the environment you discovered this bug in (run ng version)
Angular CLI: 20.2.0
Node: 22.16.0
Package Manager: npm 11.5.2
OS: linux x64
Angular: 20.2.0
... build, cdk, cli, common, compiler, compiler-cli, core, forms
... localize, material, platform-browser
... platform-browser-dynamic, platform-server, router
... service-worker, ssr, youtube-player
Package Version
------------------------------------
@angular-devkit/architect 0.2002.0
@angular-devkit/core 20.2.0
@angular-devkit/schematics 20.2.0
@angular/fire 20.0.1
@schematics/angular 20.2.0
rxjs 7.8.2
typescript 5.9.2
Anything else?
The warning originates from 300b141
angular/packages/platform-server/src/transfer_state.ts
Lines 59 to 67 in edbbbb1
It often coincides with [vite] (ssr) ✨ new dependencies optimized.
When stopping the server via Ctrl+C and re-running ng serve, the warning is gone.